3-1/4" x 2" Cast Iron Wheel Swivel Caster with 3/4" Threaded Stem - 600 Lbs Capacity3 1 4" x 2" Cast Iron Wheel Swivel Caster with 3 4" Threaded Stem Part # 7RTP032CIR Cast Iron is the standard metal wheel used by most unless a heavier capacity or greater impact strength metal wheel is needed. For applications requiring more capacity or impact strength, check out the ductile steel & forged steel wheel caster options. Please note that all 2 wide wheels are heavy duty cast iron & come with thicker treads, stronger spokes, & larger hub