Baseball hat stretcher.
There are a few other designs for 3D printed stretchers, but they all need some hardware or printed threads.

I had this cheap woodworking clamp, so I designed it around that.

Clamp face is 25mm wide x 5mm thick.

The cap needs to be wet around the perimeter, put on a stretcher, stretch and let dry at room temperature. Do not put on a heater!!!

You need print 2 pcs