referring now to the drawings , fig1 illustrates a router , designated generally by the reference numeral 100 , which is constructed in accordance with the principles of this invention . the router includes a motor housing 102 which contains a motor ( not shown ) powered through a switch 105 and a line cord 104 and having a rotating output shaft on which is mounted a collet 106 for holding a cutting tool ( not shown ). the motor , its mounting within the motor housing 102 , and the cutting tool collet form no part of the present invention and will not be described in any further detail . the motor housing 102 is supported in a base 108 , in a manner to be described in full detail hereinafter , which includes a pair of handles 110 by means of which an operator can manipulate the router 100 along a work surface . the motor housing 102 is supported in the base 108 so that the cutting tool can extend outwardly beyond the lower support surface 112 of the base 108 . in operation of the router 100 , the lower support surface 112 rests on the upper surface of the work and the distance that the cutting tool extends beyond the lower support surface 112 determines the depth of cut of the router 100 . this depth of cut may be adjusted by varying the relative longitudinal position of the motor housing 102 relative the base 108 . as is best shown in fig2 the motor housing 102 is generally cylindrical in external configuration . a first longitudinal region 114 of the motor housing 102 has a generally smooth surface , while a second longitudinal region 116 is formed with an external screw thread 118 . as shown in fig3 the base 108 has a cylindrical bore 120 which is sized to slidably receive therein the smooth longitudinal region 114 of the motor housing 102 . in order to prevent relative rotation between the motor housing 102 and the base 108 , the cylindrical bore 120 of the base 108 is formed with a longitudinal groove 122 and the motor housing 102 is formed with a projection 124 complemental thereto . the present invention is concerned with the arrangement for adjusting the depth of cut of the router 100 . accordingly , there is provided an adjustment ring 26 which engages both the screw thread 118 on the motor housing 102 and also rotationally engages the base 108 . since the motor housing 102 cannot partake of rotational motion relative the base 108 because of the groove 122 and the projection 124 , rotation of the adjustment ring 126 effects longitudinal displacement of the motor housing 102 relative the base 108 , which varies the distance that the cutting tool projects beyond the lower support surface 112 . subsequent clamping of the adjustment ring 126 to the motor housing 102 and the base 108 maintains the desired depth of cut adjustment . thus , the adjustment ring 126 is formed with an internal screw thread 128 ( fig5 ) which is complemental to the external screw thread 118 of the motor housing 102 . the base 108 is formed with an annular groove 130 at its upper end and the adjustment ring 126 is formed with an inwardly directed projection , or flange , 132 which engages the annular groove 130 . accordingly , rotation of the adjustment ring 126 does not affect its longitudinal position with respect to the base 108 but due to the pitch of the screw threads 118 , 128 , the motor housing 102 is longitudinally displaced . preferably , the adjustment ring 126 is a split ring hinged at 134 , as best shown in fig4 and 5 . each half of the adjustment ring 126 is generally semi - circular in plan . this allows for economical molding of the adjustment ring 126 and easy assembly onto the router 100 . the adjustment ring 126 is preferably molded of a plastic material so that it is inherently resilient . after the adjustment ring 126 is rotated to achieve a desired depth of cut , the ring 126 must be clamped to the motor housing 102 and the base 108 to maintain that depth of cut setting . toward that end , the adjustment ring 126 is formed with a first projection 136 adjacent a first of the opposed ends flanking the split of the ring 126 and a second projection 138 adjacent the other opposed end flanking the split of the ring 126 . preferably , the projections 136 , 138 are mirror image halves of a frusto - conical structure . when pressed together , the projections 136 , 138 provide a recess 140 which holds the head 142 of a threaded member 144 against rotation . a circular clamp knob 146 is provided . the knob 146 has an internally threaded boss 148 which is threadedly engaged with the threaded member 144 , as is best shown in fig7 . the clamp knob 146 has an inner camming surface 150 which bears against the frusto - conical surfaces 152 , 154 of the projections 136 , 138 , respectively . thus , clockwise rotation of the clamp knob 146 on the threaded member 144 moves the clamp knob 146 closer to the motor housing 102 to draw the projections 136 , 138 toward each other , thereby closing the gap between the opposed ends of the adjustment ring 126 and clamping the adjustment ring 126 to the motor housing 102 and the base 108 . conversely , counterclockwise rotation of the clamp knob 146 loosens the adjustment ring 126 . since the clamp knob 146 extends away from the router 100 to a region which is free of all obstructions , it is very easily manipulated by the operator . the clamp knob 146 is circular , with the inner camming surface 150 being beveled so that it is frusto - conical . to provide substantial engagement of the inner camming surface 150 with the surfaces 152 , 154 of the projections 136 , 138 of the adjustment ring 126 , the surfaces 152 , 154 are shaped such that at a section taken along a plane orthogonal to the threaded member 144 , each of the surfaces 152 , 154 describes an arc of a circle having a predetermined fixed diameter irrespective of the position of the plane along the surfaces 152 , 154 . the center of that circle varies linearly as the plane moves along the threaded member 144 . thus , as the clamp knob 146 is tightened on the threaded member 144 and the projections 136 , 138 are moved closer together , the inner camming surface 150 always engages the same size frusto - conical surface . advantageously , the router 100 is arranged with adjustable limit stops for the depth of cut adjustment mechanism so that the operator can quickly change the depth of cut setting between first and second preset depths of cut . these limit stops are provided on stop rings which encircle the base 108 and which may be fixed to the base 108 in preset angular orientations . the limit stops cooperate with structure on the adjustment ring 126 to provide limits to the range of angular rotation of the adjustment ring 126 . fig8 - 10 illustrate a stop ring 156 which may be utilized for the above - described function . a pair of such stop rings 156 are utilized , the stop rings being rotated 180 ° from each other when in use , as will be described in full detail hereinafter . like the adjustment ring 126 , the stop ring 156 is a split ring hinged at 158 . each half of the stop ring 156 is generally semi - circular in plan ( fig8 ) while being generally triangular in cross section as can best be seen in flg . 11 . thus , the inner surface of the stop ring 156 is at an angle of approximately 45 ° . this inner surface is serrated to form a plurality of grooves 160 . the wider end surface 162 of the stop ring 156 is also serrated . the stop ring 156 is preferably molded of a plastic material so that it is inherently resilient . the stop ring 156 is formed with an interfering projection 164 at one end and an adjustment projection 166 at its other end . the projections 164 , 166 are thus opposed across the opening of the split stop ring 156 , and the spacing therebetween determines the overall circumference of the stop ring 156 . to adjust that circumference , the adjustment projection 166 is formed with an opening 168 which is directed circumferentially of the stop ring 156 . on the interfering projection 164 , there is formed a tab 170 circumferentially directed toward the adjustment projection 166 . the tab 170 includes a first barb 172 and a second barb 174 and is adapted for insertion through the opening 168 . when the first barb 172 engages the projection 166 , the circumference of the stop ring 156 is relatively large and when the second barb 174 engages the projection 166 , the circumference of the stop ring 156 is smaller . to accommodate the stop rings 156 , the lower end of the adjustment ring 126 is formed with a beveled annular surface 176 , as best shown in fig1 . the base 108 is formed with a beveled annular surface 178 adjacent the annular groove 130 , so that when the adjustment ring 126 is installed on the base 108 the surfaces 176 and 178 together form a v - shaped annular groove . the pair of stop rings 156 fit within this groove , with one of the stop rings oriented 180 ° with respect to the other stop ring , as is best shown in fig1 . to effectively fix the position of the stop rings 156 in the v - shaped annular groove , the beveled annular surface 178 is formed with a number of ribs 180 which are directed transversely to the direction of rotation of the stop rings 156 in the v - shaped annular groove . the ribs 180 cooperate with the serration grooves 160 of the lower one of the stop rings 156 when the second barb 174 engages the adjustment projection 166 so that the stop ring 156 is at its smaller circumference . in this state , the lower stop ring 156 is effectively clamped and prevented from rotating . the cooperation of the serrations on the end surfaces 162 of the stop rings 156 prevents the upper one of the stop rings 156 from rotating with respect to the lower one of the stop rings 156 when the second barb 174 of the upper stop ring 156 engages the adjustment projection 166 of the upper stop ring 156 . for cooperation with the interfering projections 164 of the stop rings 156 so as to limit the extent of angular rotation of the adjustment ring 126 , the adjustment ring 126 is formed with a tab 182 which extends toward , but terminates before , the beveled annular surface 176 , as is best shown in fig1 . the projections 164 , 166 of the stop rings 156 extend beyond the v - shaped annular groove and therefore extend into the path of travel of the tab 182 . thus , the range of angular rotation of the adjustment ring 126 is limited by the angular positions of the stop rings 156 . in operation of the limit stop arrangement just described , the stop rings 156 are set with their first barbs 172 engaging the adjustment projections 166 so that the circumferences of the stop rings 156 are relatively large and the stop rings 156 are free to rotate independently in the v - shaped annular groove . the operator then sets the greater of the two preset depths of cut . the lower stop ring 156 is then moved so that its interfering projection 164 abuts the tab 182 . the adjustment tab 170 is then manipulated so that the second barb 174 engages the adjustment projection 166 of the lower stop ring 156 . this causes the lower stop ring 156 to be clamped to the base 108 by means of the ribs 180 and the serration grooves 160 . next , the adjustment ring 126 is moved to set the shallower depth of cut . the upper stop ring 156 is then moved so that its interfering projection 164 abuts the tab 182 . its adjustment tab 170 is then manipulated so that the second barb 174 engages the adjustment projection 166 . this clamps the upper stop ring 156 to the lower stop ring 156 by means of the serrations on the end surfaces 162 . thereafter , the operator can quickly change the depth of cut between the preset deeper and shallower depths of cut , as defined by the positions of the two stop rings 156 , by rotating the adjustment ring 126 until the tab 182 abuts against the respective interfering projection 164 . accordingly , there has been disclosed an improved depth of cut adjustment mechanism for a router . while an exemplary embodiment has been disclosed herein , it will be appreciated by those skilled in the art that various modifications and adaptations to the disclosed embodiment may be made and it is only intended that this invention be limited by the scope of the appended claims .