The monorail system is the reason we call the leg irons TRI-MAX. The internal bar not only strengthens the hold vertically and laterally, but inhibits a shim from entering the nose or the rear of the shackle. It also defeats a pick if it is engaged through the keyway. While it may be possible to pop the double lock, a pick cannot go completely through the handcuff to engage the rear retaining bars and depress them. Tri-Max maintains the integrity of 1. Nose of shackle 2. Rear of shackle. 3. Key hole. That's why we call it TRI-MAX Security!