A mandrel for transporting a set of substrates includes a rod having a free end and a fixed end, the fixed end configured to be coupled to a transport mechanism. A series of spacer elements are arranged on the rod to keep the set of substrates seated on the rod in respective fixed positions with a last spacer element nearest to the fixed end. A notch is arranged on the rod between the fixed end and the last spacer element configured to catch a substrate that becomes unseated from the last spacer element.