Head Gasket Shim - 4.100 in Bore - 0.015 in Compression Thickness - Rubber Coated Steel Core - Small Block Chevy - Each MPN - R2 FOR CAST IRON OR ALUMINUM HEADS . GASKET BORE 4.100. The coating on this gasket has been changed to a clear silicone Vendor FEL-PRO Truck Freight-- NO