As always, make sure bdsm/kink play is safe, sane, and consensual. Never leave your sub alone during bdsm play. Especially with CBT, it’s important to test devices on yourself first before using them on your sub. You can’t be a very good Dom if you have no idea what it feels like. Chances are you’ll either go too extreme or bore your sub to tears. Actually either extreme of that spectrum could have your sub in tears, whether through pain or boredom. Always keep one very important rule in mind when planning and participating in a session: If you break your sub, you don’t get a new one!  ;)

Measure the length from the end of the wood clamp (where the ends are angled) to the first screw.

Measure and cut four 3/4 inch velcro strips of the length you measured in step 1. All 4 strips should be cut from the rough side of the velcro, not the soft side that the rough side is designed to stick to.

Peel the backing of one velcro strip and place it in the area of your wood clamp that you previously measured, from the end all the way to the first screw. Be sure the long side of the strip is as close to an edge as possible. Repeat with a second strip on the same side of the clamp, and 2 additional strips on the other side of the clamp. See the photo below for an example. Make sure all of the velcro strips are on securely, and it's probably a good idea to let them sit for a while with the clamp left open before closing the clamp.

Be sure to have an object in place at whatever level your sub's dick is at.

Place the clamp on the object (such as a chair) with the clamp opened around 2 inches wide

Carefully place your sub's dick in the clamp

Turn the handles to close the clamp until your sub can feel the prickly feeling velcro, or to your desired level

 Put your sub's soft dick in the clamp, then close the clamp so it doesn't quite touch your sub's dick. Then if/when he gets hard, he will feel the "spiked" feeling of the velcro. You can use this as a deterrent for your sub getting hard, if he was told not to.

Put your sub's soft dick in the clamp, close the clamp so it almost touches your sub's dick, then lay a vibrating wand over the clamp so it's right on the head of your sub's dick. Then kick back and watch the show. ;)

You could also close the clamp on your sub's hard (or soft) dick so he's already feeling the velcro pressed up against his dick, then add a vibrating wand laying on top of his cock head to see how much bigger his dick can try to grow. As a result, it will will press up against the velcro even more.