This is the Park Tool CNW-2 Chainring Nut Wrench. The CNW-2 makes chainring bolt set installation and removal easy. It securely holds the slotted nut to prevent spinning when tightening or loosening the bolt. Double-ended to fit most slotted-type nuts. The outer width of both ends of the CNW-2 are nominally 12mm wide. One end has a two outer tips nominally 2.7mm wide each, and the other end has tips of 3.8mm each. The blade thickness is nominally 1.35mm.