Head Bolts have under-head radius, to prevent premature stretch and failure. Superior 190, 000 PSI material delivers greater strength than competitive bolts. Bolts are for small block Chevys and are longer than stock for use with head bolt washers (#MAN42102-34 sold separately). One package services one cylinder head (two packages required to complete engine).Pit Stop USA offers Manley Superior Head Bolt Set - SB Chevy 42171 at low everyday prices. Be sure to check out all of our products from Manley Performance including Manley Performance Cylinder Head Bolts.