Super simple universal rail filament roller guide.

You will need to print:
1x Bracket
1x Ring
2X Spacer

Hardware you will need:
1x 608 bearing
1x M3 x 22mm bolt
1X Bolt & T-Nut combination for mounting bracket to the rail. I used M5 Hex cap head bolt with M5 T-nut.

Top Mount version is designed for M4 14mm bolt and M4 T-Nut.

Print Settings
Brim: No
Supports: No
Resolution: 0.2mm or better
Infill:20%