Eric- My C3S manual says 2" U-bolts. Assume same for C3SS as only apparent difference is shortening on elements. IIRC you and corresponded way back then when these were new. Mine also up all that time. Was good for a few more DXCC from my centre of Toronto 15.5 ft wide lot - now need 4 to finish off HR#1. 73, George VE3YV / K8HI