A lot of vintage (60/70s) garden tractors have 3/4" front spindles. A bent 3/4" rod serves as the axle and king pin. Needless to say, they don't hold up when a frontend loader is added. They continue to bend. Tractors with 1" spindles seem to do OK.
My plan is to use 1" trailer axle stubs with 1.5" square shanks and drill the shank for 3/4 grade 5 bolts as king pins. Load on the axle will be about 4" from the king pin hole. Stubs are rated for 1250# each.
How much load before the bolt bends/breaks?
--Andy Asberry recommends NewsGuy--