HAMILTON Extra Heavy-Duty Casters feature precision integrated HPI swivel technology that improves the bearings element of contact and more than doubles the number of contact points.-1/2" thick drop forged steel mounting plate. -3/8x3" plate steel legs are welded inside and outside to forged steel horn base. Sturdy 1" diameter integrally forged kingpin with mounting plate. Main HPI load bearing is 5-5/16" outside diameter with hardened raceways to 58-62HRC and ground to surface finish 16 micro inches; secondary load bearing has 1" precision tapered thrust bearing that counteracts radial thrust. -3/4" diameter axle. Ball check type lubrication fittings in swivel assembly and wheel hubs.