For use with Mortise locksets with a deadlatch positioned below the latchbolt. Compatible Locksets: Accurate, Arrow, Best*, Corbin/Russwin, Falcon (1992 M Series), Sargent (7800, 8200 & 9200 series), Yale (8800) *For Best 45H & 47H deadlatch below, and Best 34H - 37H deadlatch above. Also works VON DUPRIN 9975 (7500 mortise case)