Abstract: A thumb-knob assembly for preventing a mortise lock from being opened from the outside even by a proper key. My thumb-knob assembly may be the one shipped with the mortise lock or may be bought separately and substituted for the thumb-knob assembly that was originally installed. It affords better protection than an extra bolt or a night-latch without their installation cost, is superior in appearance, and its installed cost should be less.

Abstract: A cheap, one piece, pocketable, one hand operated, snap on or off clamping attachment for a lock bolt thumb knob for preventing the lock from being opened from the outside. One end of the attachment has connected elements that can embrace the thumb knob in either its vertical or horizontal position. The connected elements have two extended legs that spring grip the door knob hub and can bias the attachment to its operative position or hold it in its inoperative position. This cheap device takes the place of a more expensive bolt and its installation cost.