This Z-axis belt tensioner was designed specifically for my Elegoo Neptune 4 Pro, but this model can be adjusted for installation on any belt slinger that has a similar design to Z-axis frame.

Parts list (use parametrized f3d file if you want to use parts of different dimensions):

• 1x 608 ball bearing
• 2x M4x10 bolts
• 1x M4x20 bolt
• 2x M4 T-nuts
• 1x+ M4 nut
• 1x+ washer

Print:

• 1x base
• 2x bearing-skirt
• (optional) 1x spacer

Printing instructions:

• Tune your printer and material to achieve a dimensionally accurate result
• Use brim on base to prevent lifting
• No supports
• Resize spacer height if needed. I ended up not using it and used extra M4 nuts and washers to adjust bearing height

Happy printing without lose belts ;)