Allstar 0. 055 inch I. D Aluminum Hole Engine Oil Restrictor with Hex Head - Pair features engine oil restrictors that fit small block Chevy bowtie block applications. They have . 055 inches i. d. hole and are made from high-quality steel featuring an allen head. The oil restrictors replace the production oil galley plugs at the rear of the block. They restrict oil flow to the top end, forcing more oil to bearings to cut power loss from windage. They are sold as one pair and have two extra o-ring seals which are also included. They are backed by a 90-day limited factory .