I made those caps (with CATIA 3DX Cloud) for cardboards tube for the "DIY" club of 3DS Velizy Campus, this is to store drill bits !
One cap is fix, one is removable , this is suitable for internal diameter 50mm. Note that 5 little bulges are forcing the fixation to avoid cap to leave.

Printed with Ultimaker 5S using the .8mm nose and PLA material.

Models are downloadable and free to print, the 2 STL ones, and the Native 3DXml CATIA ready to be adjusted to your cardboard tube dimensions using the exposed parameters.

3DXml file to be edited with CATIA 3DX.