Shimano BB-UN300 Square Taper Bottom Bracket 68/122.5mm mens It replaces the special bolt

It replaces the special bolt on the fixed (non lever) side of your bar end shifter and adds a nice little spot to attach smallish things like motor controls

but most of the view is blocked (not recommended)

Especially sturdy when using the internal bar end handlebar mounting

For use without seat cushion

Shimano BB-UN300 Square Taper Bottom Bracket 68/122.5mm mens It replaces the special boltSHIMANO Square Type Bottom Bracket MTB Standard Structure Features: SHIMANO quality performance cartridge bearing square bottom bracket Better chainline stability with chain line stabilizer 3 structures available Standard, E type, chain case options Adapter material: Aluminum