track 130 rotates away from the first retaining leg 80 and into engagement with the second retaining leg 90 simultaneously the second track 160 rotates away from the second retaining leg 90 and into engagement with the first retaining leg 80 specifically the end portion 144 of the second arm 134 of the first track 130 engages the end portion 96 of the second retaining leg 90 the second arm 134 of the first track 130 slides along the second retaining leg 90 to a rotational position radially inward of the end portion 96 of the second retaining leg the stop surface 154 on the stop rib 152 of the second arm 134 of the first track 130 engages the second retaining leg 90 to stop rotational movement of the knob 14 in this position of the parts the first track 130 blocks inward movement of the end portion 96 of the second retaining leg 90 while the edge surface 46 or 48 of the opening 40 blocks outward movement of the second retaining leg simultaneously the end portion 174 of the second arm 164 of the second track 160 engages the end portion 86 of the first retaining leg 80 the second arm 164 of the second track 160 slides along the first retaining leg 80 to a rotational position radially inward of the end portion 86 of the first retaining leg the stop surface 184 on the stop rib 182 of the second arm 164 of the second track 160.