Correct Tap to use

[tank1949]

What is the correct tap to use for 1/4" x 28 tapered grease fittings? Should I use a NPT tap or straight wall? I must install several grease fitting in a Bravo OD. Fellow boater instructed how to drill and tap but didn't explain if tap was tapered or not.

 

[alldodge]

Bt Doctur this ones for you

 

[dwco5051]

1/4" pipe tap is 18 TPI and the hole is just over a half an inch

 

[dwco5051]

From the SAE dimension standards; " It is recommended that SAE-LT taper threads (Society of Automotive Engineers Lubrication Threads) be installed into straight holes with a 1/4''-28 UNF-3B straight-threaded hole." If you have to pre-drill the holes it takes a #3 drill bit.

 

[dwco5051]

1/4 " NPT x Zerk

 

[Old Ironmaker]

I was going to say Teflon but it's tap not tape, sorry.

 

[alldodge]

I'll add the thread is not NPT its either straight or tapered. The 1/4 NPT uses a 7/16 drill bit which makes the hole close to 1/2 diameter after taping

 

[Bondo]

What is the correct tap to use for 1/4" x 28 tapered grease fittings? Should I use a NPT tap or straight wall? I must install several grease fitting in a Bravo OD. Fellow boater instructed how to drill and tap but didn't explain if tap was tapered or not.

Ayuh,.... Standard American grease fittin's only come in 2 thread sizes,....

The smaller are plain ole 1/4"-28,... standard 1/4" fine threads,.... no taper,....

The larger size is 1/8"- Pipe thread,..... tapered pipe thread,....

 

[QBhoy]

Check the Zeus guide.

 

[tank1949]

Not much "meat" to drill via #3 bit and thread. I am guessing that I should start with a plug tap and the after threads get started, finish with bottom tap. To me, using a tapered 1/4x 28 threaded tap, would not be wise, since it would be too long and might cut into the hinge bearing surface.