Simple Lens Cap

I bought a clip-on photo lens set for my camera phone and the "macro" lens came without a cap. The wide-angle screws into it and it is expected to use that lens cap. Since I like to carry the macro lens alone I put this together. The ID of the cap is 18.5mm, depth of 4mm.

This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/0pMBbBIkZeR