Five designs for round rail end support/bracket/socket in 10 sizes:
13mm
16mm
19mm
21.5mm
24mm
25.4mm
29mm
32mm
40mm
50mm

I recommend doing a quick print of the size you need to check for fit, making any scale alterations that are required and then printing with an infill level that matches the application.
Although there is now a heavy duty version available, please check suitability if you are using them for particularly critical applications.

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