any of the teeth it should be pointed out that the shaft opening 58 is sized to permit the rectangular box 41 and the cover piece 42 rigidly fixed to the top piece 46 to tilt without contacting any portion of the vertical shaft 56 at the same time any rotation of the upper disk 92 that is needed in order for the teeth of the hirth coupling 104 to mesh precisely is also permitted this result is possible because the force of the spring 78 and the frictional resistance of the elastomeric washer 60 are chosen such that the rectangular box 41 will rotate about the vertical shaft 56 before any damage occurs in the hirth coupling 104 more particularly if the teeth of the hirth coupling do not mesh precisely a force is produced as the angled sides of each tooth are pressed against one another as the spindle moves the upper disk 92 towards the lower disk 100 this force is transmitted via the nose 70 and acts to further compress the spring 78 when the transmitted force begins to exceed the spring force produced by the compression of the spring 78 the force acting to keep the elastomeric washer 60 and flange 62 against the inside surface 64 of the cover piece 52 will diminish towards zero magnitude the spindle will keep the.