degree angled cut 150 a these dove cuts are perpendicular to one another also through support plate 150 is a passageway or hole to allow the unobstructed passage of light 150 b shown in fig1 an exploded perspective view of the back of the xy finder are threaded holes 140 a in plate 150 these threaded holes are for ball plunger screws 140 a ball plunger screw is similar in appearance to a common set screw but provides a ball plunger a miniature ball and spring the spring provides force on the ball such that the ball provides a smooth constrained force on the moving surfaces ball plunger screws 140 are utilized in both versions of the xy finder the ball plunger screws are used on the moving parts x plate 110 and y plate 120 and also frustroconical adapter 220 shown in fig1 and 18 base plate 150 also has threaded holes 33 b for machine screws 33 shown in fig1 there are 4 end plates 101 102 103 and 104 which bolt onto plate 150 these end plates serve two purposes first they act as stops for the moving parts x plate 110 and y plate 120 and also for the part barrel 220 in the xy finder generic version second these end plates also hold the positioning screw assemblies end plates 102 and 104 hold the.