15" Slim M-Lok Free Float Handguard for SM .308 RifleSteel Barrel Nut included, thread is LR 308 1 7 16 and 16 TPI 2A The distance from center of barrel nut to the top of handguard rail is 1. 325". If this distance is the same as the rifle receiver, the handguard rail will be flush with rifle receiver top rail, regardless your rifle is called high profile or low profile. 5 shims(~0. 05") included for easy indexing. ID is 1. 177". Please be aware this shim may not be big enough for every barrel. Top