Top plate is 1/4" cold forged and measures 4 x 4-1/2". Bolt hole is 2-5/8" x 3-5/8", slotted to 3 x 3". 1/4" upper and lower raceways. 5/16" load balls. 1/4" balls for lower raceway. 5/8" nut and bolt kingpin. Roller bearing. Zinc plated. FOB Shipping Point. Steel surcharge may apply. Wheel Description PAYRON - Cast iron steel. PLEXITE - Black phenolic. PAYVULC - Black mold-on rubber.