disposed within the bolt is used to bias the ring toward positions corresponding to extended and retracted positions of the bolt a catch mechanism can be provided to engage a housing and resist movement of the bolt if the bolt is forced toward its retracted position application_number US 3317979 A description an exemplary door lock 10 of the dead bolt type illustrated in fig1 through 11 of the accompanying drawings embodies many novel aspects of the present invention in general it includes a mounting 11 secured to a door 12 a lock cylinder 13 supported by the mounting a thumb turn assembly 14 supported by the mounting on the opposite side of the door from the cylinder a bolt 15 and housing 16 mounted in an edge 17 of the door in which the bolt is received the bolt can reciprocate between a retracted position within the door as shown in fig4 and an extended position in which it projects into a socket 18 in the door frame 19 as shown in fig3 the mounting 11 includes two escutcheon plates 20 and 21 held against opposite sides of the door 12 and four through bolts 22 the bolts are positioned so that their heads engage the interior escutcheon plate 21 while they are threadedly received by sockets in the exterior plate 20 a relatively large transverse opening through the door 12 is aligned with a round aperture 23 in each escutcheon plate the cylinder 13 sometimes referred to as a mortise cylinder is of conventional construction and is positioned within the door opening it is threaded to mate with the aperture 23 of the exterior escutcheon plate.