KAC-Knight's Armament SR-15 URX 4 IBN Rail Spare Shim Kit (30299)
Spare shim kit for the Knight's Armament SR-15 URX 4 IBN handguard, found here. Includes 7 shims and installation instructions.
Fits the 5.56 version of the URX 4, 7.62 shim kits are available here.