Use a screw in the small hole to make electrical connection to the battery. The screw should have an overall length including head of about 6 mm (1/4 inch) give or take about 0.5 mm. A flat head screw's head includes its length while other screw types do not. So some suitable screws are a M3x6 flat head, a 6-32x1/4 flat head, or a M3x4 round head. The screw hole size is designed to be tapped to an M3 machine thread but can be drilled out or resized to fit (e.g. using the FreeCAD file).

This is intended to be used by sliding the battery's negative terminal into this part and leaving the positive end sticking out.

Print settings are not critical. Printing vertically (as shown) will not need supports. The bottom has 45 degree chamfers instead of rounded corners to make printing easier. You may want to use a brim or remove the 1 mm outside chamfer if your setup's adhesion is low.

A FreeCAD file is provided to make it easy to adjust for a just-right fit.

The dimensions used assume the parts may print about 0.2 mm oversized. Dimensions as provided:

• The 7.1R=14.4 outside diameter should fit all AA battery applications
• The 5.35R=10.7 inside diameter is likely to fit all AAA batteries (5.3R=10.6dia could be snug on some batteries)
• The 1.35R=2.7 diameter for the screw is designed to be tapped for an M3 screw
• The 2.5 base thickness is relatively short so extra plastic from screw threads will not interfere with the battery-to-screw connection
• The 27 mm side length is not critical and may be increased or decreased a large amount as desired