Thumbturns These distinctive decorative thumbturns are offered on mortise locks manufactured by SARGENT and CORBIN RUSSWIN. They were designed at a scale that complements the decorative levers and roses offered by the two brands, and can be provided in any of 14 architectural finishes. Thumbturn SpecificationsCorbin Russwin MT1 and Sargent T1 thumbturn specification. Thumbturn SpecificationsCorbin Russwin MT2 and Sargent T2 thumbturn specification. Thumbturn SpecificationsCorbin Russwin MT3 and Sargent T3 thumbturn specification.