SHK112BLKASM on some NXT Gun Diagrams. SHK112ASMBLK on others. Located below the Bolt Guide on the rear of the Shocker are the threaded ends of two port inserts. The Port Inserts are slender rods equipped with very fine Orings. They serve to divide gas passages inside the Shocker. Correct installation of the Port Inserts requires the use of specialized pneumatic alignment equipment at the Smart Parts factory. Improper installation can damage the Port Insert seals and misalignment will prevent the Shocker from functioning. The Port Inserts and their Orings are non-wear items and do not ever need to be removed for the Shocker for anything short of body milling or anodizing. Even if someone offers you free beer and pizza, do not remove the Port Inserts.