Replacing D cells with an 18650 Battery Cell – Inspect My Gadgets
Tube Battery Adapter for 18650 ( or other ) : r/flashlight
3D Printed Battery Adapters - Want to Sell - BudgetLightForum.com
18650 Battery Adapter for 2 C Cells - 3D Printable Model on Treatstock
Aaa To Aa Battery Adapter 2aa To D Battery Converter Holder Aa To C Battery Adapter For Battery Converter Adapter Case - Battery Accessories & Charger Accessories - AliExpress
D Cell to 18650 Adapter by reibuehl | Download free STL model | Printables.com