This is a bar end plug for a BMX handlebar. Note render of .3mf looks odd since there's a  cylindrical ‘print setting’ modifier in there as well(see below).

Plug has 18mm outer diameter with a wedge that can secure into a 19mm opening.

32mm outer diameter for large end cap.  Edges are tapered for comfort - no sharp edges.

Uses a 40mm M4 bolt with nylock nut that presses into the end hex opening.  Tighten bolt to pull wedge in to secure in bar.

ASA or PETG would hold up nicely.

3 perimeters / 15% infill minimum and I used a print modifier to use 5 perimeters and 90% infill on the outer 15cm of the main body so it can take some wear(download the .3mf for these settings in prusa slicer).  You could certainly print these entirely solid too for sturdiness although you need to have your extrusion multiplier dialed in else it may push out in some areas for a less clean appearing print… though it will still be very solid! :)