[revrnd]

What is the thread on a typical grease fitting? Is it 1/4" - 20 (UNC) or 1/4" - 28 (UNF). Even though the threads appear tapered, it's not a 1/16 - 27 NPT (too big).

TIA

 

[commanderjjones]

I think it's 1/4"-28 UNF. I'll have to check the tap I used to be sure.

 

[Toxic-21]

I think it's 1/4"-28 UNF. I'll have to check the tap I used to be sure.

Jerry is correct.
You need a #3 drill bit for the hole size. If you do not have a #3, 7/32 will also work.

The holes are tapped straight, the taper on the grease zerk will take care of the sealing on the threads.

 

[Cobra_Gt]

Very important to use the correct drill bit size. My tech installing them on a ZTR mower didn't believe me. Drilled them out with what I said first, but didn't drill it correctly, didn't hold the bit straight. Then drilled a hole size recommended for a 1/4" - 20 UNC, 13/64 and broke the tap off!!!!!

Sent from my Xoom using Tapatalk

 

[revrnd]

Thanks guys, I've got the charts & know most of the tap drill sizes off by heart (I'm a retired tool & die maker). At work any items that had grease fittings were vendor sourced, so we never had to drill & tap for them.

The taper kind of threw me off. I've added the info to a little notebook that I carry in my pocket in the shop.