The file 'M4 Hex Jig 3D Printer Model' is (stl,step) file type, size is 172.8KB.
This the easiest I came up with for turning 4mm hex from 5mm round shaft.
Clamp block to trim each side in between rollers, surface will be flat after grinding 0.5mm, Good job when it fits your microbit screwdriver.
Needs 604zz bearing on m4 bolts, m3 to hold shaft in place, needlle file or similar flat abrasive, optional micrometer or caliper for precision.
collet.stl | 236.3KB | |
hexblock.step | 169.2KB | |
hexblock.stl | 405.0KB |