1/4-18 SAE tap

Pitalplace · Feb 10, 2015

I am restoring 1930 corn sheller and the 1/4" screws have 18 threads per inch not the more modern 20. Do they make such thing or will the NPT ones work? All I seem to find on the internet is the 20 tpi. and tapered pipe threads. Any ideas?

rustyfarmall · Feb 10, 2015

(quoted from post at 12:56:33 02/10/15) I am restoring 1930 corn sheller and the 1/4" screws have 18 threads per inch not the more modern 20. Do they make such thing or will the NPT ones work? All I seem to find on the internet is the 20 tpi. and tapered pipe threads. Any ideas?

I needed some non-standard sizes awhile back, and found a seller on ebay that had them. Might also try Grainger's or McMaster-Carr.

johnpop1 · Feb 10, 2015

I would try MSC or Manhattan Supply. MSC is more
likely to have them because they tend to cater to
machinists.

johnpop1 · Feb 10, 2015

I would try MSC or Manhattan Supply. MSC is more
likely to have them because they tend to cater to
machinists. McMaster Carr might have them.

AzPeapicker · Feb 10, 2015

When I checked it . it said its a pipe thread . Home
Depot sells them . &most hardware stores . Hope this
helps .

John in Az.

Mike(NEOhio) · Feb 10, 2015

Could it be a British made sheller? Then it possibly is a Whitworth thread. Diameters would be the same but with different pitch and 55 deg. angle, not 60 like US standard.

Pitalplace · Feb 10, 2015

The sheller is John Deere and it's not pipe thread. It appears that before standards it may have been common. I did find a couple on eBay and sent a message to see if they also have the die. I checked McMaster-carr and all they had was NC and NF.
Thanks guys

Leroy · Feb 10, 2015

Those screws would be 1/4" outside. The 1/4" pipe thread would be for 1/4" inside pipe diameter and outside thread on a 1/4" pipe is close to 3/8" diameter. What you are needing would be called a 1/4-18NS or national special. I did not know about the national special till a couple of weeks ago I asked on here about some taps I had that were marked NS and that is what I was told then.

Leroy · Feb 10, 2015

It was back on 1-15 on tool talk here that I asked about those NS thread cutters and it is now on page 9 here if you want to learn what I was told then about those non standard sizes.

Pitalplace · Feb 10, 2015

(quoted from post at 17:05:20 02/10/15) It was back on 1-15 on tool talk here that I asked about those NS thread cutters and it is now on page 9 here if you want to learn what I was told then about those non standard sizes.

Yea, I'm figuring it out. Thank you very much for the NS size info and I will check your post.

RGMartin · Feb 10, 2015

(quoted from post at 17:45:40 02/10/15) Could it be a British made sheller? Then it possibly is a Whitworth thread. Diameters would be the same but with different pitch and 55 deg. angle, not 60 like US standard.

1/4" Whitworth is 20 tpi, but 55 degrees.

smallercrawler · Feb 10, 2015

This may help:
Untitled URL Link

Den N Ms · Feb 10, 2015

Pitalplace,There are some on ebay
Tap

timcasbolt · Feb 11, 2015

MSC IS Manhatten Supply.

Ian Beale · Feb 12, 2015

IIRC from about 1/4 inch up NC and Whitworth will interchange

EXCEPT 1/2 inch.

Whitworth is 12 TPI, NC is 13.

And problems can result for the unwary!

1/4-18 SAE tap

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