The Howe cast caliper mounts are made of tough 8620 cast steel. 8620 is weldable, but you won't have to weld these mounts on as long as the 1/2" grade 8 bolts are kept tight on a 3" axle tube. The 4 piston versions fit any Superlite style caliper and is threaded 7/16-20. The GM version uses the same axle clamps so brake change over is easy and less expensive. The caliper bracket for the GM style brakes will fit any D52 style GM caliper and caliper bolts. The cast brackets are much more consistent than fabricated ones. Every caliper fits properly to the fixture threaded holes.