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. Our signature ""Turbo Tuff"" design combines the appropriate weight and rugged strength for ultimate horsepower applications. Each rod is shot peened after machining and magnafluxed. Bores are round and without taper. Bend and twist is tightly controlled. Like our ""Turbo Tuff"" series, our 300M rods utilize all of the same machining processes and our held to the same high standards but are made from 300M alloy. Cap fasteners are 7/16"" APR 2000 cap screws. Horsepower range for the 4340 rods is 1,250+ and 1,400+ for the 300M.