In the 1970's Joe Weider introduced the SUPER ARM BLASTER. It was a device that helped improve intensity and isolation when doing biceps (and triceps) training. In fact, photographs of all the classic bodybuilders of the era (Arnold, Lou, Zane, Coe, Columbu) would often show them training with these.
However over the years, they seemed to disappear.
Now with a resurged interest in old school training, these have returned in the form of the BT Burner.
A great device that I use every time I train arms.