I designed this socket for my new printer. It fits 3030 extrusion frame and you need, for assembly:
2x M4 nut
2x M4 bolt
2x washer
2x M5 bolt (for fix to 3030's)
M4 nut
Inserted M4 nut in the holes
Designed in Fusion360
The author marked this model as their own original creation. Imported from Thingiverse.