Basically what it comes down to is Gen 1 or 2. Gen 1 has 18x1, Gen 2 has both. 1/2x28 on the first section and 18x1 behind. So if you remove your flash suppressor and see 2 different size threads you could use either if the comp you want is available in both threads. If it is I would get the 18x1. It'll allow the comp to sit back further and cover the 1/2x28. If you go with the 1/2x28 it'll leave the larger 18x1 treads exposed and probably wouldn't have the appearance you're after plus leave the threads open to damage. Although those issue could be addressed with a 18x1 thread protector but it's also another part to buy.
