They have treaded spindles to take the adjustment for various door thicknesses and lock firmly with a grub screw. Each set comes complete with fixing screws, which are concealed for improved appearance, together with two escutcheons.For best results the centre of the knob should be a minimum of 3'' from the edge of the door. Heavy duty latches and locks are recommended for maximum efficiency see codes 18299/4'' or 18238/5''. Please note that all the knobs with this traditional black finish range can be used externally. Sold as a set and supplied with necessary fixing screws. The GRUB SCREW should locate on the ''V'' in the shaft and not on the threaded part.