The cap to my Fleshlight "Flight" cracked so I needed to make a replacement part. LuckilyThingiverse user @Nosse666 posted a cap for their pilot model, and because the "Flight" and "Pilot" have the same case I didn't have to go through the process of modeling the threads.

I added some voids in the threads similar to the original cap to reduce friction.

I added a couple of millimeters to the walls of the cap above the threads to cover the vent holes and control suction more easily. This also made it much easier to screw on the cap completely without becoming too tight to remove. I also added a 2mm chamfer to the inner edge, because there is a small protrusion at the bottom of the threads on the case. That also made it difficult to fully tighten and remove the cap printed from the design I modified.

Last I added some gear-like protrusions to make it even easier to screw on and off, as I always had difficulties with the smooth sides of the original endcap, especially when my hands were slippery.

I read somewhere the "Fleshlight Go" series cases use the same sized threads as the "Flight" series so, this cap may fit on those other models as well. Lmk if anyone can confirm this.