MPCNC Corner Block Upgrade V3, M3 Hardware

Printed, tested working. Uses M3 bolts and nuts.

PLEASE NOTE: corner block should be printed in the orientation where the main conduit hole is perpendicular to your print surface. Otherwise this part will probably de-laminate when you screw it together.

Also: dowels should technically be printed sideways so they have more sheer strength, but it's not as big of a deal.

Improvements (in my opinion) over original
- All nuts are held captive by the model itself, so you only need an Allen