SMG back cap threading

[BretG]

Anyone know the threading for the SMG/68 Special back cap? I need to get a tap.

[COMMANDERBOND]

they make thread gauges (to get the no of threads). take a smg or a.68 special to the machinist shop to try. I think the 68 special is the same size plug.

[Jordan]

Isn't it the same threading as an AR stock/buffer tube/thingy? I don't know my firearm terminology but something along those lines is supposed to thread right in.