The ring and body of this unusually strong car is investment cast of 17-4 heat treated stainless steel to provide a superior product. Compatible with "UXP" and "UTR" pole end fittings. Ring I.D. is 1.625". The RC-125 is for 1.250" T-track and has a screw lock-pin, special UHMW polyethylene slides inserts and provisions for up and down shackles. This car is NOT recommended for use with poles that are to be stored vertically up the mast.