A customer of  a Penicap Frenum gives the Frenum community a useful hint, if you have problems of irritation of the direct fixation with the Frenum shackle. The frenum can be irritated by the shackle. A way how to solve is to put a small ring in the frenum, amd pull the locking shackle through the case holes and the ring, and not anymore directly through the frenum hole.

See his comment here:

I did order a penicap that was far too small but even so your design and material means there is no slipping. Also the reality is that a frenum can’t take any pressure for extended periods of time. So the method I use is perfect for us. I use lots of hair conditioner as a lubricant to put it on and follow the fitting method you suggest. The penicap just stays in place and the lock just stays there inert but secure. I just hope my idea helps someone. You have a great concept and I know there are lots of guys out there who will get a frenum piercing but don’t want a PA. I was so disappointed initially that it didn’t work for me but we are both thrilled now. My wife can play and I stay frustrated and horny. Thanks for replying to my emails. I appreciate it.
Gavin
PS if anyone wants to ask me questions on our experience with the frenum model I’m happy for you to share my email. My main advice would be to measure very carefully before buying.