Spring tensioned roller carriage to suit 2020 extrusions. Designed to for use with https://www.thingiverse.com/thing:2640394
Wheel mount is 5mm, designed for 20mm wheels. I used random springs from my toolbox and the M3 screws holding the adjuster are 40mm
I chose to print with a brim to minimise any warping issues.
Print at your favourite settings.....just keep the infil up for strength.