Tanman is correct with his link, however the M40A3/A5 used the older legacy cans with the overlapping design. Is your barrel turned down for the olde model?
If you have some matching hick-ups get with Garin Lee at Surefire. He will get you squared away. I'm sure he will chime in sooner or later to your thread.
If you have the SOCOM 762RC you will need the SFMB-762-5/8-24 brake. That is the correct brake for that suppressor. That being said it will not be an exact clone build because the M40A5 uses the MB762SSAL/RE brake and the FA762SS-BK suppressor.