Yale 314 1/4 Double Cylinder Auxiliary Mortise Deadbolt
ANSI Code
Black Painted
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The Yale 315 is a typical single cylinder deadbolt with a cylinder on the exterior and a thumb turn on the interior.
The Yale 313ST is the same single cylinder deadbolt will they sell it around the exterior and a thumb turn on the interior however this is what's called a classroom type function where the interior thumb-turn will retract the latch bolt but will not project the last bolt from the interior side.
this function is found commonly on bathroom doors in schools where the custodian can lock and unlock the door from the exterior with a cylinder but if someone is occupying the bathroom and the cylinder is locked from the exterior you can always exit however from the interior you can never lock that deadbolt using the thumb-turn.