Ear strap adapter for CastleGrade masks

CastleGrade masks only come with around-the-head straps, with the more convenient and comfortable ear straps sold as an expensive add-on that's often out-of-stock with long shipping delays. So, here's a printable replacement in the form of an adapter that lets you use hair rubber bands or repurpose elastic ear straps from a disposable mask. The ribbed part of the strap fits the filter cover of the mask just like the stock around-the-head strap, and it's likewise adjustable to get the right tension to seal well.

CAUTION: Please be aware that this kind of mask needs the right tension to work and maintain a seal! Too littleor too much will leave gaps. I don't see any reason this should differ using the manufacturer's straps vs printed ones, but please follow manufacturer's directions for fitting and checking seal as if you were using the original straps.

The straps need to be printed in TPU or another flexible material. Print at 100% infill in whatever way you prefer (lots of walls, infill, bottom layers, whatever - it doesn't matter). The ribs are modeled on 0.2 mm height granularity so printing at 0.2 mm layer height is recommended and this is what I've tested for fit; other layer heights might not work as well.