This is a clamping NEMA 17 stepper mount for 2020 rail.
I'm using this to hold my bowden extruder.
It's a remix of the stepper mount by AndrewBCN in thing #528934, which is a also a remix.
one M3 20mm bolt and nut to tighten the clamp
one M5 16mm bolt for the 2020 rail mount
one M5 T-slot nut
OpenSCAD source file is included with proper attribution to paenian for his great original design.
Update: Version 2B has the correct spacing between the clamp and the block that fits in the 2020 extrusion.