Manley Pro Series connecting rods are forged from aircraft quality 4340 vacuum degassed material. Each rod is fully machined in the Manley Lakewood, NJ factory to the highest standards. Each rod is shot peened after machining and magnafluxed. Bores are round and without taper. Bend and twist is tightly controlled. Cap fasteners are 7/16" APR 2000 cap screws. Horsepower range for the 4340 rods is 1,250+ and 1,400+ for the 300M.