Questions for Engineers About Barrel Threads

[Ian_Gere]

OK so what I want to know is the tech specs of the common or garden 14mm CCW thread so that I can, at some point, cut them myself.

I looked up the standard pitches of threads and my research turned up Coarse 2.0 / Fine 1.5 / Extra Fine 1.25, but looking at a muzzle thread it looks like 1mm between thread crests and measuring it bears this out: 10mm = 10 gaps. Does that mean that they have 2 Starts so 2.0 is correct, or are they a special 'super-dooper-fine' 1.0?

Also I'm guessing that you need a left-hand die to cut a CCW thread, right? Or can you cut either way just by turning a die that way? If I am right, how difficult/expensive is it to get a left-hand die?

May as well turn this thread (fnah fnah) open to general discussion of flash hiders, suppressors, compensators, adapters and their various sized threads...

 

[TacMaster]

A while back I made a foray into threading my MP5's outer barrel for 14mm where the 16-14mm adaptor screws in. I made a test thread adaptor and it didn't work with the coarse die and tap I had used. I was in fact told by the technician that it needed a fine thread to work with the outer barrel and any muzzle pieces like flash hiders or suppressors.

 

[Ian_Gere]

Ahhh, well that is heading towards making sense, but the standard "Fine" pitch is 1.5, not 1. And typically now that i want to put the table i'm quoting into this thread i can't find the fucker :lol:

 

[Lozart]

Get yourself a thread gauge.

 

[Ian_Gere]

Mate, I have a vernier callipers so I know that the pitch is 1mm, but what i need to know is what this is called so that I can buy the correct die to cut it. Because none of the standard Course, Fine, & Extra Fine for M14 threads are 1.0 - well just get an M14 x 1.0 die, right? Well, not necessarily. What if it's a 2 Start thread?

Do you know whether CCW threads can only be cut by a CCW die, or can you get dies which cut both ways?

 

[Cheeky vimto]

Mate, I have a vernier callipers so I know that the pitch is 1mm, but what i need to know is what this is called so that I can buy the correct die to cut it. Because none of the standard Course, Fine, & Extra Fine for M14 threads are 1.0 - well just get an M14 x 1.0 die, right? Well, not necessarily. What if it's a 2 Start thread?

Do you know whether CCW threads can only be cut by a CCW die, or can you get dies which cut both ways?

Dies only cut in one direction. If you think about the way the thread spirals it will be going the same way if you flip it.

 

[Cheeky vimto]

http://www.rdgtools.co.uk/acatalog/14MM-x-1.0-SPLIT-DIE--CARBON--LEFT-HAND--fine--1290.html

 

[Ian_Gere]

http://www.rdgtools.co.uk/acatalog/14MM-x-1.0-SPLIT-DIE--CARBON--LEFT-HAND--fine--1290.html

Legend! Thanks

 

[Cheeky vimto]

Legend! Thanks

Don't forget you'll need a die wrench!

 

[RR01]

When you do start cutting the thread, use a bit of light oil on the barrel to stop the metal tearing and to allow the die to move back and forth smoothly. Once you've cut about 4mm of thread, check it has taken properly before cutting the rest by trying to screw on a flash hider or similar. So long as it starts and takes up the threads then you know the process is going properly and you can continue to cut the rest and finish the job. If it isn't right then you won't have ruined 1cm of barrel that you'll need to cut off to start again.

 

[Lozart]

Mate, I have a vernier callipers so I know that the pitch is 1mm, but what i need to know is what this is called so that I can buy the correct die to cut it. Because none of the standard Course, Fine, & Extra Fine for M14 threads are 1.0 - well just get an M14 x 1.0 die, right? Well, not necessarily. What if it's a 2 Start thread?

Do you know whether CCW threads can only be cut by a CCW die, or can you get dies which cut both ways?

A thread gauge would tell you the tpi straight off though. Either way it looks like you're sorted now.