Cardan Joint for Infento

This cardan joint is pretty strong. The red part in the center is a piece of an ordinary 30x30 square steel profile (length 20-30mm).
I have inserted some hat bushings in the bores as I am afraid the plastic can wear out quickly. The bolts are modified M8 bolts. Their ends were turned down to an M6 thread. They are held on the inside by M6 locknuts.