I work for a company that sells a lot of extrusions in the flooring industry. I managed to twist the bosses arm into making dies for a 45*45. 45*90,90*90 extrusions. We also had a rail support made for round bar that slots into the T slot, but needs to be screwed in from the opposite side. My latest arm twist is a tslot table but it is only134mm wide.You can use the Sbo 16 uu/20/25 round linear bearing. Works quite well and is fairly cheap compared to square rail. Hope this helps