Carbine Combination Knob & Classroom LeverCarbine Combination Knob Classroom Lever 60mm 70mm backset. Sandown 4012 Rosehill with 6012 Classroom Lever. Carbine have developed the combination knob and lever set in various functions. It's a combination of the round Sandown 4000 knob series on the outside and the lever of the Rosehill 6000 series on the inside. As such, it is a tiebolt function. Function Outside Opened by knob when unlocked. Key locks or unlocks outside knob but does not retract