Thank you sactroop,
So am I correct that the back cut I keep reading about is not the definitive way to decide if a M7 is a military contract or commercial produced bayonet? And if there is there a way, how would you decide if you were looking for a military issue production M7? I noticed that there are small nuts versus the threaded hand guard. Is this a military or commercial feature? My Imperial/colt came with two 11010068 grips with two separate small black nuts.
The back cut, in and of itself, is not a good indicator of whether an M7 is US military, foreign aid, or commercial. However, if you have a BOC, Conetta, or FZR; they will always have 90° back cuts and are all US contracts. (you've already found out what happens when I use the word "always") Milpar US military contracts will have a 90° back cut and those are always considered US military, but they made thousands of curved run out blades that are not supposed to be US contract M7s.
If you have an Imperial M7 (not Colt), the 1973 contract will have a 90° back cut, but the the military began to allow the curved run outs after that, so the later 1976 and beyond contracts will have curved run outs, and are US contract, but you cannot be sure. Imperial made bayonets for other countries as well.
Ontario and General Cutlery will have the curved run outs and were produced for US contracts as well as commercial and foreign customers. You cannot tell the difference unless there is a welded cross guard (remove the grips), then you know for sure they are commercial.
The grips held together by screws and nuts are found on the Imperial/Colts. They are also found on Eickhorn produced M7s. The rest of the M7s use the " threaded bushings" glued into the grips.
So if you want to be sure you are getting a real US military M7 bayonet, find one of the US contractors: Milpar, Conetta, BOC, FZR, and Imperial with a 90° back cut.
To help with the timeline, other than the Eickhorn made Colt M7s, all the other Colt marked M7s pre-date the aforementioned contractors. Hope this helps.