Restrictor Plate Inserts -. Tapered inserts are machined to be within.002 Inch for precise tuning. Inserts feature a step to simply drop into spacers and have sizes engraved on each insert for easy identification. Sold in a set of 4. Inserts for 1 Inch Restrictor Plate. Details: Finish: Natural Color: Natural Material: Aluminum Sold As: Each Product Description: Restrictor Plate 1 in Thick 4 Hole Square Bore Aluminum Natural Sold Individually Specialty items for the Shop, Trailer and Track. The Allstar Performance brand offers thousands of hard-to-find, specialty items that cover many segments in the performance aftermarket. For over 30 years, customers worldwide have come to rely on the quality, affordable and practical items available from Allstar Performance.