Abstract: A voluntary closing prosthetic prehensor includes a locking mechanism which may be locked into any position, and released with a small amount of force. With locking enabled, the prehensor opens and closes normally until the user applies sufficient tension to the prehensor cable after the prehensor has closed upon an object. Then, a lever arm attached to the cable rotates, pulling a second cable which causes an elliptical cam to rotate such that its wider portion presses against a pawl, causing the pawl to rotate into engagement with a toothed sector, locking the prehensor closed. When the user releases the force on the cable, the lever arm is biased to return to its normal position, but the prehensor stays closed because the pawl remains engaged with the sector. The cam includes a ratcheting drum which takes up the slack in the second cable. To release the prehensor, the user applies a small amount of force to the first cable, moving the lever arm and pulling the second cable, which rotates the cam.