Technical Foundation
What Is a Grease Fitting Kit?
A grease fitting (zerk fitting) is a small, threaded nipple installed into a bearing housing, pivot point or bushing that accepts a grease gun coupler and contains a spring-loaded check ball, allowing grease to be pumped in under pressure while sealing against contamination and grease backflow between servicing intervals. Kits bundle an assortment of common thread sizes and angles — straight, 45-degree and 90-degree — since equipment designers choose the fitting angle based on the clearance and grease gun access available at each specific lubrication point.
Thread size and pitch must match the tapped hole exactly; metric (M6, M8, M10) and SAE/UNF (1/4-28, 1/8-27 NPT) fittings are common but not interchangeable, and cross-threading a mismatched fitting damages both the fitting and the housing threads. Button head fittings use a larger-diameter, rounded head designed for use with a button-head grease gun coupler in tight-access locations where a standard coupler can't get a straight approach to a conventional fitting.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Thread Size | Metric (M6, M8, M10) and SAE (1/4-28, 1/8-27 NPT) | Must match the tapped hole exactly — metric and SAE threads are not interchangeable |
| Fitting Angle | Straight, 45°, 90° | Angle is chosen based on grease gun coupler clearance and access at the specific lubrication point |
| Head Style | Standard hex-drive vs. button head | Button head fittings suit tight-access points needing a button-head coupler for a secure connection |
| Check Ball/Spring | Internal spring-loaded ball valve | Seals against contamination ingress and grease backflow between servicing intervals |
| Material/Finish | Zinc-plated steel, stainless for corrosive environments | Stainless resists seizing/corrosion in wash-down or outdoor exposed equipment |
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Applications
Where Grease Fitting Kits Get Used
Grease fitting kits are specified anywhere a bearing, bushing or pivot point needs a replacement or new zerk fitting for routine lubrication.
Heavy Equipment & Construction Machinery
Grease fitting kits maintaining pivot points and bearing housings across excavators, loaders and dozers.
Agricultural Equipment Maintenance
Assorted fitting kits replacing damaged or clogged zerks on tractors and implement grease points.
Automotive & Fleet Maintenance
Replacement grease fittings restoring chassis and suspension lubrication points to service condition.
Industrial Machinery & Conveyor Systems
Grease fittings maintaining bearing lubrication on conveyor rollers and drive shaft pillow blocks.
Marine & Trailer Equipment
Stainless grease fittings resisting corrosion on wash-down exposed trailer axle and hitch points.
Manufacturing Plant Maintenance
Grease fitting assortment kits keeping general maintenance stock on hand for varied equipment thread sizes.
FAQ
Grease Fitting Kits Questions, Answered
How do I know what thread size grease fitting I need?
Remove the old fitting if possible and measure or compare its thread against a thread gauge, or check the equipment manufacturer's parts documentation for the specified fitting size. Common sizes include metric M6, M8 and M10, and SAE 1/4-28 and 1/8-27 NPT — an assortment kit covering multiple common sizes is useful when servicing equipment from different manufacturers.
What's the difference between straight, 45-degree, and 90-degree fittings?
The angle determines how the grease gun coupler approaches the fitting relative to the housing surface — straight fittings work where there's clear perpendicular access, while 45-degree and 90-degree fittings are used where surrounding components block a straight approach. Match the angle to the physical clearance at each specific lubrication point, not personal preference.
Why won't grease flow through my zerk fitting?
A clogged or damaged internal check ball/spring is the most common cause — dirt or hardened old grease can jam the ball, or physical damage from impact can deform the fitting. Replacement is generally faster and more reliable than attempting to clear a clogged fitting, since fittings are inexpensive and designed as a serviceable wear item.
What is a button head grease fitting used for?
Button head fittings have a larger, rounded head designed to mate with a button-head grease gun coupler, which is useful at tight-access lubrication points where a standard coupler can't get a straight, secure connection to a conventional fitting. They require a button-head-compatible grease gun coupler to use properly.
Should I use stainless steel grease fittings?
Stainless fittings resist corrosion and seizing significantly better than standard zinc-plated steel, which matters most on equipment exposed to wash-down, marine environments, or continuous outdoor weather exposure. For general indoor or moderate-exposure equipment, standard plated steel fittings are typically adequate and more economical.
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