referring again to fig3 an aperture 110 extends through the entire thickness of door 104 to closely accommodate therein shaft 210 extending from combination input knob 206 into a space 214 defined inside casing 208 located in correspondence with aperture 110 in door 104 in casing 208 there is provided an annular journal bearing 216 to closely receive and rotatably support shaft 210 via 266 projecting therethrough into space 214 casing 208 is conveniently formed e g by machining molding or otherwise in known manner to provide a pair of guide slots 218 218 which are shaped sized and disposed to closely accommodate lock bolt 212 in a sliding motion between its locked and unlocked positions while an important object of this invention is to provide its locking function in a highly compact manner which inherently necessitates the selection of strong materials for forming the casing 208 and lock bolt 212 guides 218 218 and lock bolt 212 must be shaped and sized to provide the necessary strength to resist any foreseeable brute force to open door 104 persons of ordinary skill in the art are expected to know of suitable materials for such purposes for example although the safe walls and door may be made of highly tempered steel or alloy the lock bolt itself may be made of a softer metal such as brass or an alloy such as u201c zamak u201d and so may other elements of the mechanism as also illustrated in fig3 within space 214 inside casing 208 there are also provided attachment.