Designed for high security  with the Medeco Key and cylinder, the SL-M Tri-Lok is the perfect solution to protect the shaftway door interlock release key hole.  All Tri-Lok SL-M Medeco models bear the U.L. label.  Security, simplicity, and good appearance are all part of the Tri-Lok Elevator Door Safety Plug Locks.  All Tri-Loks install in a single 7/8" hole, and the outside face is only 1-1/8" in diameter by 3/32" thick.  The SL-M Safety Locks mount through 1" to 1-3/4" thick slide doors.  It is reliable and unobtrusive.