Grease Fitting Thread Tap Size??

[Pooh Bear]

I have an ORC on my tractor. It has two grease zerks.
The ORC stays on the tractor all the time.
And this leads to sometimes loosing a grease zerk.
This last time I lost one and I can't get a new one back in the hole.
The threads just won't start and it needs to be re-tapped.

Are grease zerk threads a standard size, or do I just take one with me
and get a tap for it. And a couple of plugs so this doesn't happen again.

I mite have a tap for it if I just knew the size.

I'm not looking forward to the day I have to remove/change this ORC.
Had a hard time getting the roll pin in there.
Probably never get it back out again. So I need to keep it greased.

Thanks.

Pooh Bear

 

[Anonymous-0]

Some zerks are 1/4-28. (.25 dia)
Most are 1/8-27 NPT (.406 dia max)
Take it with you if you don't measure it ahead of time.

 

[Pooh Bear]

There seems like a lot of difference between 1/8 and 1/4.
Maybe I could mic the threads and see which one it is?
Looks like it is probably the 1/4-28 size.

Thanks.

Pooh Bear

 

[Anonymous-0]

Some Zerks are drive-in too. I just replaced one on my brush hog that was a drive-in.

 

[old]

There are 3 or 4 standard sizes for zirks. Most of the ones I have seen on ORC I believe are 1/4 inch.
Hobby farm

 

[Anonymous-0]

The ORC uses a 1/8 inch pipe thread zerk. When you remove it the hole is large enough to drive the roll pin out the other side.

 

[TimW(PA)]

There is a big difference in thread nomenclature that really confuse people who have never worked with plumbing or pipe fixtures. Normally American SAE threads are measured by determining the actual diameter of the bolt and then counting how many threads per inch i.e 1/4 / 20. This bolt has a diameter of a 1/4 inch, and 20 threads per inch. Same goes for metric, excpet the pitch is the actual distance measureed from one thread to the next i.e 10 x 1.0 . This bolt would meausure 10 mm thick with 1mm between threads.
Pipe threads are diferent. They measure or refer to the inside diameter of the pipe, because in in fluid dynamics you are concerned with what volume a certain pipe will carry not its outside diameter. So a fitting for a 1/4 National Pipe Thread (NPT) is actually going to be nominally closer to 1/2 inch or so after you accomodate the wall thickness of the pipe. Add to this, that the common pipe threads NPT are tapered. This is so that as the fitting is tightened they get wedged together and form a seal.
There are also National Pipe Straight (NPS) threads that are the same thread pitch as NPT threads except they are straight and dont do the taper thing.
this brings us to Zerk fittings. If you look at a common zerk fitting you can see it is a tapered thread with 20 threads per inch (TPI). I searched one time thru every industrial supply catalog I could find, as well as online and I could never find a tapered pipe tap that small. Every rescource I could find said to use a 1/4 20 SAE tap. It works fine. Zerk fittings do come in different sizes too so you'll have to get the right ones.....You probably knew all this, but maybe it'll help someone in the archives someday.....Tim

 

[TimW(PA)]

Oops Yeah it should be the 1/4-28 size not the 1/4-20. 1/4-20 is the normal coarse pitch hardware bolt size...sorry

 

[JMOR]

Small NPT taps do exists. #1, somebody had to tap all the equipment out there. # 2, I have in my hand as I type this both a 1/4 NPT tap and a 1/8 NPT tap 20371(4401)from Vermont American Tool CO. Lincolnton, NC 28093-0340.

And for the record, I note that you said couldn't find, not that they do not exist.

That was a good explanation of pipe vs bolt sizes, as you recognize, many do not know.

 

[souNdguy]

TSC makes a zerk tool with a thread chase / tap and wrench, and extractor all built into one.

I've used it to clean buggered threads.. and to make threads in soft metal.. like aluminum.. etc..

Soundguy

 

[TheOldHokie]

(quoted from post at 05:18:16 08/29/07) this brings us to Zerk fittings. If you look at a common zerk fitting you can see it is a tapered thread with 20 threads per inch (TPI). I searched one time thru every industrial supply catalog I could find, as well as online and I could never find a tapered pipe tap that small. Every rescource I could find said to use a 1/4 20 SAE tap. It works fine. Zerk fittings do come in different sizes too so you'll have to get the right ones.....You probably knew all this, but maybe it'll help someone in the archives someday.....Tim

NPT thread standard - smaller sizes:

1/16-27 NPT
1/8-27 NPT
1/4-18 NPT

There is no taper pipe thread that uses 20 TPI. Smaller NPT taps are all readily available - try McMaster Carr or MSC online - they both have an extensive selection.

WRT zerks they come in all manner of threads - NPT, NPS, BSPT, BSPP, SAE, Metric , etc. You have to gage them to know what you have. If it is 20 TPI with a major diameter of .250" it's almost surely 1/4-20 UNF.

TOH

 

[TheOldHokie]

Make that if it's 20 TPI its likely 1/4-20UN. If it's 28 TPI it's likely 1/4-28UNF. If it's tapered and you think its 28 TPI better get a thread gage. It's likley 27 TPI and NPT. You can't eyeball the difference in 3-4 threads.

TOH

 

[Pooh Bear]

Actually, I think I found a solution.
I have a package of zerks I bought to replace the broken ones with.
I have replaced them before. Still have some in the package.
So why don't I just look on the package and see what it says.
Or take it with me to get the tool. I check out TSC and see what they got.
And while I'm there I should get some plugs so I don't keep breaking zerks.

Thanks for all the info.

Pooh Bear