I know, I know. This thing looks like a medieval torture device, but after 2+ years of flawless performance, it is anything but.
Sleeves never slip out and I’ve never felt the teeth.
Upfront: I only use the Pro-Strap with the H1 and H2.
Each “tooth” is slightly beveled, and all you have to do is sand off any 3D printed errors around the corners, depending on your printer’s quality. Not too smooth, just sand it until you can run it along the skin on the bottom of your forearm and not feel any raised edges or any discomfort.
There are two versions, the Large and Small Tooth.
I would use the Small Tooth version on softer or thin-walled sleeves like the Gen2, Silk, and Core. The large tooth is the best gripper and excellent on thicker walled sleeves like the Gen1 and Gen3. I think either version is safe on any sleeve except the core, it’s the only one I could feel something other than the sleeve itself, which is why I made the smaller toothed version, and even then, it just made the Core too stiff.
I make no guarantees as far as safety, there are a ton of different 3D printers and people have different levels of experience when it comes to printing, which is why I haven’t shared this yet. But after 2+ years and not one incident, I feel it’s safe for anyone who is smart enough to use a 3D printer 
. I imagine if you just use the forearm test to prep your prints, you’ll be good to go if anything actually did go awry.
The first couple of times you use it, choose some slower scripts and take the time to check your strap’s tension and check for any slippage. Then do the same with faster scripts. I mastered the minimum tension in about 5 mins. It is infinitely better than the bare strap, and the lower tension required (especially on the Gen3) keeps the sleeve from squeezing all the lube out.
I use INDUSTRIAL strength velco to mount the small part to the handy 1 and Handy 2 sleeve adapters. DON’T use cheap velcro options. The other section just slides onto the strap. There is no top or bottom on each part, they are mirrored.
Personal use: I would start using this with the Gen3, the outer bumps on that sleeve make it the perfect entry level sleeve for this device. Also, I’ve only ever used Handy’s PRO-STRAP, the original Handy 1 strap is just, well, poor. But I’ve used the H1 and H2 with these grippers Hands on, Hands Free, standing, sitting, laying down, fast and slow scripts. Just works like a charm. I have never used open-ended sleeves, so I have no idea how it works on those, use those at your own risk.
If you do decide you want to try an open-ended sleeve, I suggest this video:
https://discuss.eroscripts.com/t/princess-leia-cum-on-the-babysitters-braces/44170
Just in case
Known Failures: The only failure was a Tenga “twist” Sleeve, nothing seems to hold that thing for very long. And even in that case, the strap slipped safely upward on the sleeve, probably caused by the internal twist thing inside forcing the strap up.
H-Clasp90-Large Teeth.stl (1.9 MB)
H-Clasp90-Small Teeth.stl (1.9 MB)
