These single-pole clamps will add a new dimension to nipple play.  The threaded clamps are adjustable to each persons delight from soft, medium to painful, whatever works for you.  :)

Rimba Electro Clamp. This item has a 3.5mm male audio jack and fits directly into all 3.5mm female audio plug-ins on power boxes.

Each individual clamp is uni-polar, but together in use these clamps are bi-polar.

The bars will expand to almost 1" and is 1" across.  

Tip: use water based contact gel to experience the best results.

NOTE: Be careful and cautious playing with nipple toys, especially if you have any heart problems, heart transplant, or other medical conditions dealing with the chest.  Moving current across the chest could prove to be dangerous in certain situations.