The handle is actually part of a bowflex (not mine), but you could use a piece of PVC or wooden dowel rod which is the other piece. Some nylon laundry rope, a small carbiners clip, a small eyebolt, washer and nut, a large washer with a small hole and a one inch flat head wood screw with glue.
Like I say I don’t really like the roller type movements, but it’s great for wrist curls. I do em palms up and down siting on a bench with my hands hanging off my knees. This will be poo pooed by some, but it works fine for me at the end of a back workout when the forearms are already pumped from all the gripping.