B7 Battery end tube

thingiverse

This is the end tube to fit the Bulgin battery holder into. It comes in two different lengths depending on which battery holder you choose to fit. The Bulgin BXS002/1 takes 2xC cells. The BXS001/1 takes 1xC cell. This is a design choice, if you need a higher voltage for your circuit then use 2 cells. If you can get away with a lower voltage, get the shorter holder. Put 26500 lithium-ion cells in them and you get 3.6 to 4.2 volts or 7.2 to 8.4 volts. 2 cells with the higher voltage will last longer but 1 cell is cheaper.