This mounts a paddle or toggle switch on a drop handlebar within easy reach of the hoods and drops. It can be used for electronic shifting or electronics control with a momentary switch, or it could be used for lighting with a latching switch.

I use it with a momentary SPDT switch on my Archer Components MFR Drop bar remote for easy electronic shifting.

It mounts on top of the bar tape and is held on by a common rubber O-ring or rubber strap left over from a computer or light mount. It will fit at least a 4mm wide O-ring. Garmin recommends using only EPDM O-rings for their mounts. Nitrile/buna-N O-rings are more susceptible to UV and ozone damage and probably should not be used. Viton O-rings might be fine for this application.

This mount fits a paddle switch approximately 13mm wide and 7mm deep for a 6mm (1/4") panel mount hole. Search under "toggle switch" on Digikey. As of early 2022, there one waterproof SPDT momentary switches that will fit priced at $12 each. I used an inexpensive, non-waterproof switch.

This prints fine without any supports, but ironically, the ramped washer probably fits the 8mm nut better when printed with an overhang, as shown in the photo, otherwise you will need to use a knife to clean up the wider bottom layers, like I did. But because it's a small piece, make one in each orientation and see which you prefer.

I have included the Fusion 360 part file so the part can be customized. Most notably, the KludgeOversize parameter is used to make holes or inside cutouts larger since my 3D printer isn't well calibrated. I tried to parameterize everything, but started getting sloppy farther into the part.