TinyMight 2 - stem cap

0.16 layer height recommended.

The tolerances are quite tight - hopefully they work for your printer.

But if not, you can copy and modify this CAD project: https://cad.onshape.com/documents/2ece09fa20b0f89300a13527/w/d7c97470a4a118c67a7d3c9f/e/c5e2350ed016f4f60dbf8a7e
Check the base sketch and modify the inner ring diameter (defaults to 11.9) to set the desired dimension. Recommend changing it by ~0.1

Optionally check the oring sketch and modify the distance from the center of o-ring to the outer wall (0.3 by default).