I know people hate me for getting into little issues like laws. If you want a semi-auto "STEN", buy the gun complete from Catco. You will have a legal semi-auto carbine that resembles a STEN.
If you buy a parts kit from a selective fire STEN (and those are the only kits I know of right now) and make up a receiver tube for it, you will have manufactured a machine gun.
If you are either ignorant or stupid, and want to tell me how it's all legal and no problem, and so-and-so who sold the tubing said you can make a "real" STEN, etc., save it for the Feds.
Jim
(Yes, there are some pure dummy MG and SMG receivers that cannot possibly function as a gun. Anyone who believes people are buying tubing to make dummy guns will be interested in buying the Bay Bridge from me.)
JEK