I love to rock climb and recognized how big a role forearm and grip strength come into play. I use a typical grip trainer but thought I could build a forearm trainer on my own for very cheap. Now the simplest way to do this would be to find a piece of wood, stick, dowel, timber etc. And drill a hole into it through the stick in the middle, tie a rope to it and then to a rock. But I wanted something strong and light, and that looked decent.
Now I decided to do this after-the-fact I made this trainer. So the pics aren't that detailed and step-by-step, but it's really simple and I trust you can do this rather easily. So, now...what you'll need:
1- 12" piece of PVC 2" in diameter
1- worm gear stainless steel pipe clamp to fit around PVC
1- length of rope about 4'
1- swivel clip
Step 1: Connecting rope to PVC
Pretty simple, just slide pipe clamp onto PVC near as center as possible. Then feed one end of the rope between PVC and clamp. And tighten clamp with a screwdriver or hex key. Don't go crazy so you don't cut into the rope and damage it.
Now I like to burn the ends of synthetic rope to prevent fraying and also it makes the end a little bigger so it can't slip knots easily.