2020 Tee T bracket

A sturdy 90 degree tee for joining two 2020 extrusions using four tee-nuts. I ended up making two slightly different variants of the body to suit the machine screws I had lying around:

* 2 off M3 x 8 pan headed for joined piece; 2 off M4 x 8 countersunk for cross piece

* 4 off M4 x 8 countersunk

Can be printed with no supports when stood on the square end.