“D.O.T”. 3″ high x 2″ diameter. All brass. “D.O.T BREVETS DESCALLES” is stamped on the obverse of the body. The reverse of the lock is blank. There is a spring loaded lever on the base of the padlock to change the combination. This padlock appears to be a prototype. “DOT” stands for “Defiance of Thieves”.Patent #1006366. US Patent #1393269.