PM couplings (otherwise known as Paper Mill couplings) are gear couplings designed for high misalignment and short shaft separation applications typically found in paper mills. Standard gear couplings are made from Carbon steel where PM couplings are manufactured from alloy steel and nitrided for better wear characteristics. Standard gear couplings are designed for a static angle of 0.5-1.5 degrees where the PM coupling is designed for 6 degrees.