This is a cap for Armattan screwdrivers (1.5mm, 2mm, 2.5mm and 5.5 box). Those screwdrivers come without cap so this one will allow you to keep some screw or any spare part inside the screwdriver.

The inside of the Armattan screwdrivers is Ø14mm. You can probably edit my design to fit other screwdrivers.

Part has been designed on Solidworks 2018, file is available to download.