The units we've seen have a threaded muzzle on the shroud that, while it's 1/2x20 UNF thread, the threads stop short of the shroud and the moderator's endcap doesn't seat flush to the shroud and clipping occurs. This can be remedied by putting a shim between the endcap and shroud. McMaster-Carr has appropriate spacers that would work if you want to go that route.