The Stovebolt Site Forums The Shop Area Driveline Help - Zerk Tap Size?

There is some thread damage on a spindle hole for the Zerk fitting. The Zerk fitting is the larger 1/8" NPT (I believe that's correct) which uses a 7/16" hex wrench or socket. I'd like to touch up the spindle threads with a tap. Not sure which tap size to order from McMaster-Carr. What is the correct tap for these this Zerk fitting?

Thanks,
-Mike

A standard 1/8 npt thread tap should get you what you are looking for. You should be able to get one at a local hardware store. It may be necessary to grind off some of the thread lead to get the depth required as these are probably tapped npt thread short

And I have it correct that the Zerks on the spindles are the 1/8 NPT, not 1/4 - 28 taper?
Looking again at McMaster-Carr I now see the "1/8 NPT 27 TPI" under the Pipe and Conduit section. Tap diameter is 0.332 which seems correct. They don't carry a bottoming chamfer so yea, I might have to grind off some of the lead. Wow, $35 per tap! Hopefully, available at local HW store.

Yes, everything has gone up! Let us know how it turns out.

Wow! Home Depot lists them for a bit over $6. $35 is crazy expensive. There aren't Taper, Plug or Bottoming taps for pipe taps, just for straight thread taps, so you'll need to grind the end off if it doesn't clean up without doing that.

[on edit] Rocky's Ace Hardware in Concord has them for $9.

It appears no one here has ever heard of short projection pipe taps for shallow holes

https://www.mcmaster.com/products/short-projection-taps/

If grinding a pipe tap bear in mind to maintain clearance angles similar to sharpening a twist drill to prevent breaking off teeth in your part.

Curt,
You're right, I had never run across those short projection pipe taps. But for what Mike is trying to do (freshening up existing pipe threads), there's no need for lead-in chamfers on the tap. The taper of the tap and the existing hole will let it start just fine. And if he bottoms out in the hole grinding off some of the tip will work as well, with no need to worry about chamfering. But that tap won't work for threading new holes. The $6-9 taps I found would be better than $35 in my book.

I have made my own "plug" and "bottom" taps for years by modifying regular taper taps, which are usually a lot less expensive than the 3-tap "sets" that are available. "Thread chasers" can also be made from taps too dull to make clean threads in unthreaded holes by using a sanding disc to blunt the tops of the threads. That prevents cutting a thread oversize when it's necessary to clean up rusty or damaged threads. A rechargeable, variable speed drill motor makes short work of thread chasing.
Jerry

I found the correct tap at a local hardware store for $8.95. Much better price!! Was able to clean out the spindle threads.

-Mike