https://bitbucket.org/malhan-designs/x301-mods/src/master/Rear Pulley Brackets - 3mm/
These rear pulley mounts compliment the Composite XY Brackets by changing the pulley holes to use M3 screws.
If you have the standard 5mm ID pulleys, print 2x of the pulley spacer to convert from 5mm to 3mm.
Derived from: