Grease Fittings Information and FAQ

Grease Fittings

Button Head Fittings

Ball Type Fittings

Pin Type Fittings

Leakproof Grease Fittings

Flush Fittings

Flow Stop Fittings

Safety Vent Fittings

Hydraulic Shut Off Fittings

Drive Type Fittings

Thread Forming Fittings

Breather Fittings

Relief Vent Fittings

Vent Fittings

Oilers

Oil Reservoirs

Drive Oilers

Oil Cups

Hole Covers

Grease Fittings

Grease fittings, also known as grease gun zerk fittings or grease nipples, serve as lubrication points on bearing housings or other mechanical components. Their design provides a secure connection to a grease gun coupler for delivering precise amounts of grease into bearings and other moving systems.

• Offered in steel, Monel®, and stainless steel materials
• Available in bright dip, passivated, zinc clear, and zinc yellow finishes
• A wide range of grease fittings is available to fit a variety of applications.

Button Head Fittings

Button head grease fittings are a heavier duty fitting identified by their flat, low profile appearance. They are able to handle large grease volumes due to their high flow rate and sturdy construction. They are commonly used on conveyors, mining equipment, agricultural equipment, and other rugged applications.

• Flat head design minimizes damage from debris
• Quickly connect and remove grease gun for faster servicing
• Easily greased using a button head coupler
• Both metric grease fittings and inch size grease fittings are available.

Ball Type Fittings

Ball type grease fittings are a reliable solution for any application requiring frequent lubrication. They are identified by their smooth, dome-shaped nipple and feature a ball check valve that reduces backflow when grease is applied.

• Serviced using push type grease fitting couplers
• Available as straight ball grease fittings and as 45° angled or 90° angled grease fittings
• Hex wrench holds allow for simple installation

Pin Type Fittings

Pin type grease fittings use a cross pin to create a positive lock with a special coupler to provide a leak‑proof connection during servicing. Pin type grease fittings were one of the first styles of grease zerks manufactured and are still being used for vehicle restorations and other applications where positive lock coupling is desired.

• Available in zinc clear, zinc yellow, or traditional steel
• Original equipment replacement for early model vehicles
• Simple servicing when used with pin type couplers

Leakproof Grease Fittings

Leak‑proof zerk fittings prevent lubricant leakage using a plastic, rubber, or brass seated steel ball check. Intended for light oils and hydraulic fluids, leak‑proof grease zerks are often used in the textile and food processing industries where preventing lubricant leakage is critical.

• Available in zinc clear, zinc yellow, or traditional steel finish
• Designed to provide leak‑proof seals up to 10,000 psi
• Drive in options available for efficient production assembly
• Straight and 90° pin type grease fittings are available

Flush Fittings

Flush type grease fittings are low-profile zerk fittings that excel in applications with minimal clearance tolerances between moving parts. Their low profile design makes them a great fit for shafts, pulleys, and other rotating assemblies. Since flush type grease zerks don't protrude from their mating surface like standard grease fittings, they are less susceptible to damage.

• Available in zinc clear trivalent, cadmium green, and zinc yellow
• Easily serviced using a flush type coupler
• Large diameter flush type fittings are ideally suited for high volume applications

Flow Stop Fittings

Flow stop grease fittings® control how much grease is able to flow out of the fitting. It is designed to positively shut off at a specific pressure, thus preventing over greasing and damage to seals. The fitting reopens once pressure drops within 2 psi of the stated minimum pressure.

• Equipped with a check ball to reduce risk of contamination
• Available in corrosion resistant zinc clear or zinc yellow finish
• Available as straight and 90° flow stop zerks.
• Smart technology prevents over lubrication of equipment

Safety Vent Fittings

Safety vent fittings, or safety grease fittings, are externally similar to standard grease zerks. However, they boast the additional feature of a milled vertical slot in the threads. This slot serves as an air vent while grease is being applied to a mechanical component. The slot also serves as a visual aid as grease will flow out when enough has been applied.

• Provides a visual indicator when enough lubricant is in an assembly
• Reduces risk of damage from excessive pressure build up
• Stainless steel variations are ideal for marine environments or other corrosive applications

Hydraulic Shut Off Fittings

Hydraulic shut-off fittings, also known as hydraulic grease fittings, control the grease that flows out of a fitting. It closes at a specific pressure to prevent over greasing and damage to seals. The fitting reopens once pressure drops within 2 psi of the stated minimum pressure.

• Equipped with a check ball to reduce risk of contamination
• Available in corrosion resistant zinc clear finish
• Serviced using a standard coupler

Drive Type Fittings

Drive type grease fittings, also called push in grease fittings or press in grease fittings, are ideal for low or medium pressure applications. They feature serrated or smooth shanks for installation in drilled, untapped holes. Using drive type grease zerks can eliminate tapping costs associated with threaded applications.

• Ideal for automated, high volume, assembly line productions systems
• Low volume installation made simple using a grease fitting driver tool
• Available in a variety of angles allowing easier access in hard to reach areas

Self Tapping Grease Fittings

Self-tapping grease fittings, also known as thread forming grease fittings and spin drive fittings, feature hardened threads for installation into thin, unthreaded holes. Using thread forming fittings eliminates costs associated with tapping methods and forms stronger, cold worked threads in the process.

• Ideal for high volume, assembly line applications
• Various available angles allow easier access in hard to reach areas
• Offered in clear and yellow zinc as well as passivated and bright dip finishes

Breather Fittings

Breather fittings, or breather valves, are designed to maintain proper atmospheric pressure in transmissions, differentials, gearboxes, speed reducers, and more. The simple design of these zerk fittings provides a moisture barrier while maintaining airflow efficiency and reducing debris entry. Some grease zerk breather fittings are additionally equipped with a felt filter for increased protection against contamination.

• Offered in corrosion resistant zinc clear and zinc yellow finishes
• Allows unrestricted bi-directional airflow
• Prevents gasket distortion between mating parts by maintaining proper pressure in sealed assemblies

Pressure Relief Vent Fittings

Grease relief fittings, also known as grease relief valves and grease relief vent fittings, release excessive pressure that builds during mechanical operation in bearing housings or gearboxes. As pressure increases, the internal valve opens allowing pressurized air to escape. Once pressure decreases below a minimum threshold, the valve returns to a closed state.

• Upper pressure range indicated on the top or side of the fitting
• For best performance, install above fluid level
• Side vent valves available through special order

Vent Fittings

Vent fittings, also referred to as air vent fittings, control pressure build up in a lubricated assembly by opening and closing in a pre‑determined range. As pressure increases, the spring loaded valve opens, allowing pressure build up to escape. As pressure returns to the desired threshold, the valve closes.

• Equipped with a felt liner for added protection against contamination
• Performs best when placed higher than normal lubrication level
• Available in zinc clear and zinc yellow plating for added corrosion resistance

Oilers

Machine oilers are a lubrication fitting intended for oil fill points on machinery. They are equipped with a self-closing spring-hinged lid similar to oil hole covers to keep contaminants out of oil fill holes. They are machined from bar stock with hex wrench holds, making them durable and simple to install.

• Available in Imperial sizes
• Finished in a corrosion resistant zinc clear coating
• Hole covers with 90° elbows provide easy access for lubrication

Oil Reservoirs

Oil reservoirs feature clear plastic bowls brazed to an externally threaded fitting. With increased holding capacity, they are the ideal choice for use as a central dispenser for lubrication systems. Oil reservoirs are available in varying capacities from 1 oz to 128 oz.

• Adjustable flow reservoirs allow oil to be dispensed from a drip to a steady flow
• The clear reservoir makes checking levels fast and simple
• Zinc plated hardware provides enhanced corrosion resistance

Drive Oilers

Drive oilers are often used as oil fill ports for machinery and feature a tapered shank to create a snug, press fit in drilled hole applications. Similar to oil hole covers, they feature a self‑closing lid that prevents contaminants from entering an oil hole.

• Trivalent zinc plated steel for added corrosion resistance
• Integrated shoulder reduces risk of cracking castings during installation
• Does not require threaded holes for installation

Oil Cups

Oil cups are small reservoirs that hold small amounts of oil for machinery and allow for slow, constant lubrication of moving parts. Oil cups are simple, yet reliable components that can be used in a variety of applications.

• Equipped with a self‑closing lid to reduce contamination
• Machined hex holds for simple installation
• Body and shank are brazed together for a secure, leak proof connection

Hole Covers

Oil hole covers, or flip lids, are designed for oil fill points on machinery but do not hold any lubricants like oil cups. They are equipped with a self‑closing, spring hinged lid that minimizes risk of debris entering internal machine components.

• Feature hex holds for simple installation and removal
• Finished in a corrosion resistant zinc clear coating
• Hole covers with 90° elbows provide easy access for lubrication

FREQUENTLY ASKED QUESTIONS

• Where can I buy a zerk grease fitting?
• How do grease fittings work?
• What is the most common standard size grease fitting?
• How much grease should I put on a fitting?
• How do you know when a grease fitting is full?
• Can you over‑grease a fitting?
• How to attach a grease gun to a zerk fitting
• How to grease a zerk fitting
• How to remove a grease gun from a zerk fitting
• What to do when a grease gun is stuck on a zerk
• What size thread is used on a zerk grease fitting?

• How to replace a grease fitting with a grease fitting multi tool
• How to remove a broken grease zerk
• How to remove or free up stuck grease fittings
• How to install a drive type grease fitting
• How to remove a drive type grease fitting
• How to install self-tapping grease fittings
• How to grease a button head fitting
• How to extend grease fittings for hard to reach places
• What if my grease fitting won't take grease?
• How to clean a grease fitting

What is a zerk grease fitting?

A zerk grease fitting (also known as a grease fitting or grease nipple) patented by Oscar Zerk in 1929 is used in mechanical systems to feed lubricants like lubricating grease into a bearing using a grease gun. It was introduced as an improved method of lubricating moving parts. Zerk fittings are permanently installed on bearing housings or mechanical components to serve as a lubrication point to feed precise amounts of grease into bearings and other moving systems. Zerk fittings come in a variety of types, such as Drive In, Rivet, and Thread Forming. They can be manufactured using brass, stainless steel, and Monel® materials.

Where can I buy a zerk grease fitting?

G.L. Huyett offers its own complete private line of Heritage Industrial® grease fittings and accessories at the lowest distributor price! We are also a Master Distributor for Alemite®, Alemite Aerospace®, and Lincoln® brands. In addition, we offer a complete line of metric and international grease fittings. If you don’t find what you are looking for, call us today to speak with our friendly, experienced sales team.

How do grease fittings work?

Grease zerk fittings work by acting as a one‑way check valve that allows grease to pass through one way, but not the other. Inside the fitting is a ball check suspended by a spring. As grease is pushed into the fitting, pressure is created against the ball check that compresses the spring allowing grease to pass completely through the fitting. When grease flow stops, the spring pushes the ball check back to its original position, closing the fitting and preventing grease from escaping.

What is the most common standard grease fitting sizes?

The most common standard grease zerk size is 1/4"‑28 SAE‑LT and is often used in automotive applications. They can also be found in agricultural environments as well as other various standard duty applications. For heavy-duty applications, larger 1/8"‑27 PTF grease zerk fitting sizes can be found.

How much grease should I put on a fitting?

The amount of grease put in a fitting depends on the size of the part to which it is attached. As a general rule of thumb, apply grease until you begin to feel resistance while pumping. Do not apply grease until it seeps out of bearing seals or other components.

How do you know when a grease fitting is full?

There is no simple answer to the question of when to stop adding grease. It depends on the nature of the mechanism and the size of the space into which lubricant is being injected. Many engineers use rules of thumb to give them a rough idea of the amount of grease required.

For example, when greasing shaft bearings the formula G = DB/10 is often used, where “D” is the shaft diameter, “B” is the bearing width, and “G” is the quantity of grease. To use this formula, you need to know how much grease your gun produces for each “pump.” Another rule of thumb is to add 2 or 3 grams per inch of shaft diameter, which often equates to approximately one pump of the grease gun trigger, depending on your gun.

In all cases, when you believe that you are approaching the maximum lubrication capacity, pump the grease gun slowly and stop when you begin to feel significant resistance. Over-greasing can decrease machine efficiency and even cause damage to parts.

Can you over‑grease a fitting?

Yes. Only apply grease until you begin to feel resistance while pumping. Do not apply grease until completely full or seeping out of the fitting or other components. Changes in temperature or pressure can cause the grease to expand causing further leaks, which can cause dirt, gravel, or other debris to collect on the exposed grease and work into the moving part, shortening its lifespan.

How to grease a zerk fitting:

While grease fittings themselves do not require grease, the part they are attached to does. To grease the part, attach a grease gun to the end of the zerk fitting and pump until you feel resistance. It is a good idea to refer to your equipment’s service manual for recommended maintenance practices when possible.

What are the different types of grease guns?

There are many different types and designs of grease guns, and we offer lever, pistol, cordless, and pneumatic grease guns. We have a gun for practically any application. G.L. Huyett offers the following on our site.

Lever Gun

Our standard lever gun is not only economical, but also provides the most volume per stroke as compared to other manual guns. A full range of interchangeable / customized features are available to suit your individual needs. ** Lever guns require two hands to operate. **

Pistol-Grip Gun

Pistol-grip grease guns are good for use in close-clearance areas. Using just one hand, grease is pumped via a simple squeeze. Pistol-grip guns typically dispense less grease per stroke than a standard two-handed lever gun.

Cordless Gun

Cordless grease guns use rechargeable Lithium-ion batteries for complete portability and ease of use. Huyett grease guns come equipped with a carrying case and two batteries for extended use. ** Cordless grease guns are trigger operated, portable, and convenient. **

How to attach a grease gun to a zerk fitting

1. First, ensure both the zerk fitting and the grease gun coupler are clean and free of debris and other contaminants. This will help ensure a secure connection between the fitting and the coupler.
2. Next inspect the fitting to ensure there is no damage. If the fitting is damaged, you may want to consider replacing the fitting before continuing.
3. Once everything is clean and inspected, set the coupler at an angle to the fitting and while firmly pressing down, roll the coupler onto the fitting. You should feel the coupler clamp down on the fitting and click into position.

How to remove a grease gun from a zerk fitting

1. Ensure that the pressure has been relieved between the coupler and the grease fitting.
2. If this does not happen on its own, tilt the grease gun coupler to approximately 15 degrees to break the seal. You may see grease expelled from between the coupler and the grease fitting.
3. Once pressure is released, continue tilting the coupler past 15 degrees while at the same time twisting back and forth.
4. This should safely disengage the coupler from the fitting.

What to do when a grease gun is stuck on a zerk

Getting your grease gun stuck on zerks is not unusual. It often happens because the fitting is blocked and a pressure build-up prevents the release of the coupler. The easiest solution is to unscrew the flexible hose attaching the coupler to the gun. The pressure is reduced and removing the grease fitting should become much easier. If it doesn’t, try rotating the coupler with fingers or with pliers.

What size thread is used on a zerk grease fitting?

There are several components of threads on a grease fitting.

• Thread Series
  Thread series is the thread "style" of a given grease fitting. There are many different thread series and each has specific attributes. Thread series can be either SAE Standard (also called taper thread), American Standard, Unified National, or Foreign Standard.
• Thread Size
  Thread size is the nominal size of pipe that the fitting mates with. Originally, the size referred to the inside diameter of the pipe at a time when pipes had very thick walls. That is why a 1/8" pipe has a 0.393" actual outside diameter. G.L. Huyett carries sizes ranging from 0.18" diameter to 0.820" diameter and 6.0mm to 16.0mm in metric.
• Thread Pitch
  Thread pitch refers to the distance "peak-to-peak" of each thread. Imperial and British standards call out threads per inch, while Metric standards specify thread pitch in millimeters.

How to replace a grease fitting with a grease fitting multi tool

1. Place the socket end of the tool over the grease fitting nipple so that the tool fits securely against the fitting's hex holds.
2. If the socket end does not work, or the fitting is broken, loosen the fitting by inserting the extractor bit into the center of the fitting. Drilling out the fitting may be required.
3. Using the socket or extractor, rotate the multi-tool counterclockwise to loosen the fitting.
4. Continue to loosen the fitting until it is free from the mating component.
5. Clean the threads of the mating component with the tap end of the multi tool.
6. Thread the new grease fitting into the mating component by hand.
7. Use the socket of the multi tool to finish tightening the grease fitting.

How to remove a broken grease zerk

1. Locate an appropriately sized end wrench or use a grease fitting multi tool that fits the hex holds of the grease zerk.
2. Position the tool around the hex shaped section of the grease fitting.
3. Loosen the grease zerk by rotating it counter clockwise with the wrench.
4. Continue to loosen the grease zerk until it is completely free of its mating assembly.

How to remove or free up stuck grease fittings

Stubborn grease fittings that are broken or unable to be removed with a socket or wrench can be removed using the extractor bit of a grease fitting multi tool.

1. If necessary, begin by drilling a hole into the stubborn fitting to allow the multi tool's extractor bit to fit inside.
2. Be careful not to drill completely through the fitting as this could deposit metal shavings or other debris into the attached part.
3. Once the fitting is completely removed, clean the threads using the tap on the multi tool.

How to install drive type grease fittings, push in grease fittings, and press in grease fittings

1. Ensure the grease fitting is the proper fitment for the hole to which it is being applied.
2. Place a grease fitting drive tool over the top of the grease fitting.
3. Place the shank of the grease fitting into the hole, ensuring it is perpendicular to the mating component.
4. Tap the protruding end of the driving tool with a hammer to drive the fitting into the desired hole.
5. Continue driving the grease fitting into the hole until it is seated securely in place.

How to remove a drive type grease fitting

1. Use a slide hammer with a locking plier attachment to clamp to the end of the grease fitting.
2. Operate the slide hammer with several solid strikes to loosen the fitting.
3. Continue this action until the fitting is completely removed from its mating component.

How to install self‑tapping grease fittings

Self‑tapping grease fittings, or thread forming grease fittings, can be installed using either a pre‑existing or freshly drilled hole.

1. For new applications, start by drilling a hole into your part that is slightly smaller than the outside diameter of the grease fitting shank. It is encouraged to test fitment on a spare piece of material before permanently installing the fitting. For replacement, start on Step 2.
2. Test fitment.
3. Insert the shank of the fitting into the hole and begin tightening by hand while ensuring the fitting is perpendicular to the part it's being attached to.
4. Use a grease fitting multi tool to finish the installation. Continue tightening until the grease fitting is seated securely against the mating surface of the part.

How to grease a button head fitting

Button head fittings are popular in rugged applications where damage to protruding grease fitting heads is likely to occur. These low profile fittings can be greased using a button head coupler. Pull the coupler over the head of the grease fitting and pump until you feel resistance.

1. Ensure you have a button head coupler attached to your grease gun.
2. Clean the button head grease fitting of any contamination or debris.
3. Slide the button head coupler over the grease fitting so that the grease fitting is interlocked with the coupler.
4. Begin pumping grease from your grease gun until the desired amount has been applied.
5. Remove the grease coupler from the fitting by sliding it away from the grease fitting.

How to extend grease fittings for hard to reach places

Grease fitting extensions are used to provide additional clearance for grease fittings in hard to reach areas. Grease fitting extensions are designed with external threads on one end and a flare with internal threads on the other. To install grease fitting extensions:

1. Thread the non-flared end of the extension into the grease fitting hole of the mechanical part you are servicing.
2. Thread the grease fitting into the flared end of the extension using a socket, wrench, or grease fitting multi tool.
3. Tighten the fitting until the grease fitting and extension assembly are secure.

What if my grease fitting won't take grease?

If your grease fitting won't take grease, check the following:

• Is the fitting nipple damaged? If so, replace the fitting.
• If the fitting is not damaged, is the opening of the fitting obscured by dirt or other debris that could prevent grease from flowing into the fitting? If so, replace the fitting.
• If there are no contaminants, try using an unblocker tool to loosen any hardened grease that could be obstructing internal fitting passages.

How to clean a grease fitting

Grease fittings tend to collect dirt and debris. Using grease caps is a preventative step in keeping grease fittings clean. However if grease caps are not in use, a lint free cloth can be used to wipe the fitting clean.

For clogged or blocked grease fittings, a grease fitting unblocker tool can be used. A grease fitting unblocker is specially engineered to quickly and easily unplug stubborn grease fittings. To operate, a light weight oil is injected into the tool’s reservoir. A plunger is then inserted and a tap from a hammer injects oil into the fitting, loosening the internal components.

Learn more about how to install and maintain grease fittings.

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