taps and dies - course, fine, uss, pipe and ???

J

joe_m

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I just spent an hour drilling and tapping #10 sized holes in the end of 3/8" rods. It went so smoothly now that I've dialed in the lathe. Of course when I was done and went to put the screws in the holes they didn't fit because I was using a 10-32 tap and the screws I had were 10-24. ##$^!!!

That led to an impromptu cleaning of the tap/die drawers. I've only got about 50 dies but I seem to have about 30 pounds of taps. I printed out a few online articles about the different types - pipe threads, NC, fine etc but I'm still stuck on a few. I've got one that says it's 1/2-13 NC, and another that says 1/2-13 U.S.S. Am I right in thinking that these are one and the same, just that the U.S.S. one was made sometime before the designations were changed? And does that work for anything else I come across that's marked U.S.S. - I just look at the actual size and that will determine if it's fine or coarse? Or is a 1/2"-13 U.S.S. from the good-old days when an inch was longer/shorter than it is today?

And for the pipe taps - I'm finding them marked "pipe", NPT, NPS, and I think one that just says PT. Is there anyway else to tell these apart from the regular taps besides the obvious ones where it says 1/8" and yet it's fatter than my thumb? Are any of them usable for non-pipe applications? I've never threaded a pipe in my life and don't anticipate ever doing so - so I'm inclined to toss them all in a bag and bury them on a shelf somewhere.

thanks
Joe
 
Joe,

It seems that over the years, various standards organizations have updated the terminology and also made slight updates to various tolerances and definitions for "class of fit". The major players were the ASME and SAE. USS was the United States Standard and was incorporated into what we now have. The basic 60 degree profile hasn't changed but the major and minor diameters might be off by a few thou here or there.

I believe there is a NC (National Coarse), NF and NEF (extra fine) but in later years, it was called UNC, UNF and UNEF for "Unified". There are other designations too such as NFCJ... I gave up trying to keep track of it all.

Anyhow, those taps are probably pretty old (late 1800's to early 1900's possibly) and if I had some, I'd keep them for historical purposes.

Ray



joe_m said:
I just spent an hour drilling and tapping #10 sized holes in the end of 3/8" rods. It went so smoothly now that I've dialed in the lathe. Of course when I was done and went to put the screws in the holes they didn't fit because I was using a 10-32 tap and the screws I had were 10-24. ##$^!!!

That led to an impromptu cleaning of the tap/die drawers. I've only got about 50 dies but I seem to have about 30 pounds of taps. I printed out a few online articles about the different types - pipe threads, NC, fine etc but I'm still stuck on a few. I've got one that says it's 1/2-13 NC, and another that says 1/2-13 U.S.S. Am I right in thinking that these are one and the same, just that the U.S.S. one was made sometime before the designations were changed? And does that work for anything else I come across that's marked U.S.S. - I just look at the actual size and that will determine if it's fine or coarse? Or is a 1/2"-13 U.S.S. from the good-old days when an inch was longer/shorter than it is today?

And for the pipe taps - I'm finding them marked "pipe", NPT, NPS, and I think one that just says PT. Is there anyway else to tell these apart from the regular taps besides the obvious ones where it says 1/8" and yet it's fatter than my thumb? Are any of them usable for non-pipe applications? I've never threaded a pipe in my life and don't anticipate ever doing so - so I'm inclined to toss them all in a bag and bury them on a shelf somewhere.

thanks
Joe
Click to expand...
 
Thanks. I found enough "new" ones to not worry about the antiques. I'll just put the real old ones aside. I'd still like to figure out what the pipe taps are good for - I found a tapered one. And I've got one regular tap now that just says 18 18 on it. It's bigger than 1/4 and smaller than 5/16 but I haven't put a mic to it yet. I haven't found that size listed anywhere. I also have to go back through the pile of 1/4-20 because I had a few that says 14-20 and I assumed that they were 1/4-20 but the manufacturer forgot to add the /. Well I googled something else and found out that there is an old size 14-20 which is close to 1/4 but not the same so I have to go dig those out and put them aside before I grab the wrong one.

on the plus side - I found a couple 10-24 taps so I don't need to run into town and buy 10-32 screws.

Joe
 
I am guessing that the U.S.S ones will be compatible with the NC ones. Best way to check would be to grab a standard fastener of the same pitch and thread it in.

As far as pipe threads, you can tell them because they are tapered. Now, I know that machine taps are tapered on the ends, but pipe taps will be tapered over most (all?) of the length.

I have a few pipe taps, and have only used them once or twice, but I was glad I had them when I needed them. Pipe sizing is pretty odd, especially when you look at "1/8" pipe. One of my teachers explained it like this.

Back in the early days, before there were many standards, somebody decided it would be a good idea to have sizes that were interchangable. So they decided that all pipes would have a wall thickness of a certain amount, and that was that.

Pretty soon people started realizing that having the same wall thickness for all pipes wasn't a great idea, larger pipes needed thicker walls, smaller pipes could be made with thinner walls. There were also cases where pipes needed to handle higher pressures, and so have thicker walls; but you still want to use the same taps/dies. Basically it's a mess. Nominal pipe size can vary wildly from the actual size. It is especially dramatic on 1/8" pipe (which has an id closer to 1/4").
 
NPT, NPS

NPT = tapered your more typical pipe fittings.

NPS = straight, the few places I have seen them used is for electrical fittings like lamp sockets, lamp hanger bars and stuff like that. They are also used on some thru-hull fittings used on boats.

PT - is probably tapered but who knows
 
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"Billy G"
 
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