Lip extensions are for center hung doors, thick doors, or other conditions that vary from the "standard" 1-3/4" thick door that closes flush (or near flush) with the jamb face. Specified with electric strike by the last dash number which varies the door centerline to jamb edge dimension in 1/8" increments. For existing 7100 Series Electric Strikes, a thin metal membrane in the standard lip can be drilled or punched out and the lip extension can be added in the field. The dash number for lip extension is the same as door centerline to jamb edge dash number on complete strike.