Fancy using a bottle cap as your stem cap?
Probably best to use an aluminium top cap when you are mounting the stem, but after thats bolted up this can be swapped. Use the standard bolt, and clip the bottle cap on after. Its quite a tight fit, and cant guarantee it won't break if you try and remove again.
I printed in ABS, but I imagine any material would be fine.
Bottlecap_Stem_Cap_marked.stl | 253.1KB |