What Size Are Grease Gun Fittings and Couplers?
Most grease guns have a 1/8 in NPT thread where the coupler screws on, and that size is the same across nearly every coupler we compare. The zerk fittings on your equipment come in several thread sizes, but the ball-style head is standardized enough that one hydraulic coupler grips SAE and metric zerks alike. So the size to check is the coupler thread on your gun, then the reach and pressure rating you need.
LockNLube GC81011Best overall
LockNLube GXCLBest for recessed fittings
Akeoil XUC-05Best 6-jaw gripTwo different sizes people mix up
When someone asks about grease gun fitting size, they usually mean one of two things. The first is the thread where the coupler attaches to the gun. The second is the zerk fitting, the small nipple on a bearing, joint or axle that receives the grease.
These sizes are unrelated. The gun thread is a pipe thread, while zerks come in several thread sizes that matter only when you replace a fitting on the machine. The coupler sits between the two and only has to match the gun on one end and grip the zerk head on the other.
The grease gun thread: 1/8 in NPT
Nearly every manual, pneumatic and battery grease gun uses a 1/8 in NPT female thread at the outlet. NPT stands for National Pipe Taper, so the thread is tapered and seals as it tightens. That is why you wrap it with thread sealant tape or paste if it weeks to weep grease.
Every coupler on our best grease gun coupler page lists a 1/8 in NPT thread. That includes the LockNLube GC81011 and GXCL, the Akeoil XUC-05, the luckywagon LW-GGC-1 and the THINKWORK W6301 kit. If your gun is a common model, you can shop on features instead of thread size.
If a gun uses something unusual, such as a different thread or a proprietary hose end, check the manual first. A pipe thread adapter can sometimes bridge the gap.
Zerk fitting sizes on your equipment
Because the head design is shared, a standard hydraulic coupler works on SAE and metric zerks. The LockNLube GC81011 and GXCL list SAE and metric Zerk compatibility, and the THINKWORK W6301 lists DIN, SAE and metric fittings.
| Fitting type | Common thread | Where you see it |
|---|---|---|
| SAE zerk | 1/4-28 taper | Older US cars, trucks, farm and shop equipment |
| Metric zerk | M6x1 | Smaller joints and newer vehicles |
| Metric zerk | M8x1 or M8x1.25 | Common on European and Asian vehicles and machinery |
| Metric zerk | M10x1 | Larger joints and some heavy equipment |
| Pipe thread zerk | 1/8 NPT | Some industrial machinery |
Coupler diameter, length and reach
For a tight angle, a 90 degree adapter can help more than extra length. The THINKWORK kit includes one, along with needle tips.
- LockNLube GC81011: 3.5 in long, a good general-purpose size.
- luckywagon LW-GGC-1: 3.5 in long, with a dual-handle design.
- LockNLube GXCL: 5.5 in long, with over 3.5 in of reach for shielded PTO shafts, axles and U-joints.
| Coupler | Thread | Pressure rating | Length |
|---|---|---|---|
| LockNLube GC81011 | 1/8 in NPT | 10000 psi | 3.5 in |
| LockNLube GXCL | 1/8 in NPT | 10000 psi | 5.5 in |
| luckywagon LW-GGC-1 | 1/8 in NPT | 12000 psi | 3.5 in |
| Akeoil XUC-05 | 1/8 in NPT | 12000 psi | Not clearly listed |
| THINKWORK W6301 | 1/8 in NPT | 12000 psi | Not listed |
How to pick the right one
Work through these steps in order and you will rarely buy the wrong part.
If you want help narrowing options on a budget, our best grease gun for the money page shows complete guns that already include a coupler.
- Confirm your gun's outlet thread. If it is 1/8 in NPT, any coupler listed above will thread on.
- Look at the zerks you service. SAE and metric heads both work with a standard hydraulic coupler.
- Check how recessed the fittings are. Choose extra reach or a right-angle adapter if they are buried.
- Match the pressure rating to the job. Stubborn or partly blocked fittings suit the higher 12000 psi ratings.
- Decide whether you want a locking coupler. It stays on and frees both hands for pumping.
- Consider a rebuildable design if you grease often. The LockNLube GXCL includes a rebuild kit.
Safety notes
Grease guns build very high pressure. Wear safety glasses, because a coupler that slips can spray grease at speed. Never point the gun at your skin. Grease injected under the skin is a medical emergency, even if the wound looks small, so get care right away.
Stop machinery and let moving parts come to rest before you grease. If you work under a vehicle or raised equipment, support it with proper stands, not just a jack. If you use a pneumatic gun, disconnect the air before changing couplers.
Frequently asked questions
Do I need different couplers for SAE and metric zerks?
Usually not. A standard hydraulic coupler grips the head of both types. Check the product listing, since some list SAE and metric support explicitly.
Is a Milwaukee grease gun coupler thread different?
Most grease gun couplers, including those for battery guns, use 1/8 in NPT. Confirm in your gun's manual, because our data does not cover individual gun brands.
Can I use a pipe thread tape on the coupler?
Yes. Because 1/8 in NPT is a tapered pipe thread, a small amount of thread sealant tape or paste helps stop leaks at the gun end.
Why does my coupler keep popping off the fitting?
The coupler may be worn, the zerk may be damaged or clogged, or the pressure may be too high for a basic coupler. A locking coupler with a higher pressure rating often solves it.