Floor Door Stop-Security FS18 is designed for areas of high vandalism. The molded rubber is flame resistant and mounted to a 5/8" threaded mounting shaft. Once the 7/8" diameter hole is drilled to a depth of 2-1/2" it can be grouted in concrete and leaves no exposed fasteners. The recommended grout is Thorogrip. They are ideal for jail or security cell areas. There are two versions of this door stop one projects 1-1/2" (FS18S) out of the floor and the other 3" (FS18L).