Abstract: A jig (11) for removable fitment along the edge of a door (19) which provides a suitable combination of guides and stops to allow the location and operation of suitable cutting tools such as drills or routers. The jig comprises a pair of parallel guide plates (26) the distance between which is adjustable for removable fitment to opposing surfaces of the door. Guide holes (30, 31, 32) are located in the guide plates through which a drill or other suitable tool may be inserted. The jig has guide means (12) associated therewith for allowing location of a suitable tool at the edge of the door for making a cylindrical hole or for machining a mortise therein for receiving the body of a mortise lock or a rebate for receiving the face plate of the lock mechanism. A guide block (50) to facilitate accurate drilling is also disclosed.