The MS1861 lies horizontally in the bottom rail of ultra-narrow stile doors which have insufficient vertical space for a lock, or tempered glass doors which have no stile at all. The hardened steel cylindrical bolts allow simple drilled strike holes of a relatively small size to minimize the nuisance and danger presented by some threshold strikes in collecting debris or snagging on high-heeled shoes. 360° turn of key or thumbturn projects or retracts bolt(s). Key can be removed only when bolts are in a positively locked or unlocked position. Lock accepts any standard 1" length, 1-5/32" diameter mortise cylinder with MS® cam such as the 4036 Mortise Cylinder or thumbturn such as the 4066 Thumbturn, available separately. Lock accepts cylinder from either or both sides.