How do you measure threading for dies/taps?

[aznriptide859]

Question for you MechE/machinists out there - what's the proper way of measuring the threading of a pipe in order to match it for a die/tap?

 

I ask since I'm planning to cut down my APS 870, and I need to rethread both the magazine tube and the pump assembly. I know matching the die to a RS 870 won't work, since the shells aren't exactly 12GA, so I think I'll have to find the exact threading myself and order the correct die. I know vaguely the things I have to measure (ID/OD, pitch/inch, etc), but which measurements do I need precisely in order to order a die?

 

Thanks in advance

[shmook]

I've never seen one so don't know how how helpful This post is, but you can buy thread gauges for measuring

[DEVILHUNTER]

As Shmook sugest, there are thread gauges to measure the pitch:

 

http://www.ctctools.biz/servlet/the-544/MACHINIST-IMPERIAL-BSW-55%3F/Detail

http://www.ctctools.biz/servlet/the-545/MACHINIST-METRIC-60%3F-/Detail

http://www.ctctools.biz/servlet/the-633/MACHINIST-SAE-60%3F-THREAD/Detail

 

Also for diameter:

http://www.ctctools.biz/servlet/the-518/METRIC-RING-PLUG-GO/Detail

http://www.ctctools.biz/servlet/the-517/METRIC-THREAD-PLUG-GO/Detail

 

But you can also measure them without the gauges. Just with a carliper (and if you want, some screws). Take the carliper and measure the distance between the high part of two teeth (separated, to minimize the error) and divide it by the number of teeth in between. If you get something very near to 0.5, 0.7, 0.8, 1, 1.25, 1.5, 1.75, 2, etc milimiters the thread is metric, just measure the diameter of the male thread and you are ready to go (if you get something like 9.9, its 10 obviously). Now take an standar metric screw and check if the thread is the same.

 

If the thread is imperial, you must measure the diameter and transform it to fraction of inches. Then measure how many teeth you have per inch in the thread. For example, if you measure 1.05-1.1 mm of pich, that means you have an imperial thread of 24 theads per inch.

 

The RS should be imperial (USA made..) but I believe the APS may be metric (in the other post they talked about metric screws). By the way, once you measure it, tell us to compare. My tanakas have M25x1 in the tuve and M29x1 in the pump.

[aac]

Devilhunter as nicely explained "how to" measure a thread.

but i understand you are also asking wich dimensions are neccesary for correct identification of the thread.?

 

its the outside diameter and  the pitch. an example M12x1.75 (metric)  1/2"-13 (unc)

[Dacascos]

Got to be careful also as pipe threads can often be tapered and it really depends on what kind of pipe also...

 

You have the basic, Metric, UNC and UNF threads but also AN etc, then course and fine of all of the above. a pitch gauge and measuring the bore is easy enough. The explaination above it great but be careful as some metric and imperial threads are so very very close BUT not the same ya know 

[ED-SKaR]

A good tap and die set will come with a thread pitch measurement tool. These have a whole bunch of little metal plates, each has a line of teeth that are spaced the same as the pitch they measure, and each one in the series has a different pitch.

 

Might look like this:

 

 

for the diameter you should measure it with a calliper.

[Mike 8-{>]

Sorry for coming a bit late to this but I hope I can add a few useful comments. The tool that hasn't been mentioned which greatly aids thread identification is an engineers reference of some kind. In the UK the "Zeus book" is a ubiquitous engineering pocket reference with thread tables for most of the more common thread forms. If you want a weightier (far more comprehensive and expensive tome) Machinery's Handbook cannot be recommended too highly. The thread reference tables give you the dimensions of threads so when you measure one you can check against the table to see what it might be.

Bear in mind that most airsoft parts are likely to be metric rather than imperial. The vast majority of threads are "prefered" or standard sizes so if the numbers you measure don't match exatly to what you think the table says then look at a different thread form/type table. That said some threads are custom jobs and getting taps and dies will be prohibitively expensive.

 

I did find this rather handy reference for identifying threads http://mdmetric.com/tech/tict.htm (caution.it is rather yellow)