Manley "H" Beam connecting rods are manufactured from 4340 forgings to the same exacting standards developed and approved by Manley original equipment customers. There is a vast difference in quality between a Manley "H" Beam and the "other" inexpensive H-Beams on the market. Weight matched to +/- 1.5 grams. Perfectly round big and small ends. Bend and twist is tightly controlled. Cap fasteners are 3/8" ARP 2000 for the H-Beam and H-Tuff and 3/8" ARP Custom Age 625+ for the H-Tuff Plus. H-Tuff and H-Tuff Plus Series have a heavier beam for higher boost applications.