limited by the length of the bolt 778 within the recess 776 the bolt 778 rotates and slides with the switch cam 770 the stop button 766 is mounted within the tubular recess 776 formed in the knob 758 and encloses the end of the bolt 778 located in the recess 776 and the spring 780 see fig9 the stop button 766 can axially slide within the recess 776 towards or away from the switch cam 770 the range of outward axial movement of the stop button is limited by stops 782 each engaging with an inner step of the knob 758 the head of the bolt 778 directly abuts the underside of the stop button 766 depression of the stop button causes the bolt 778 to be pushed through the base compressing the spring 780 moving the switch cam 770 away from the crank 768 and knob 758 connected between the knob 758 and the crank 768 is a long helical spring 784 the helical spring 784 locates in a circular channel 790 formed on the underside of the knob 758 as best seen in fig1 one end abuts against a wall 792 at the end of the channel 790 the other end abuts against a stop not shown formed on the crank 772 the spring 784 rotationally biases the knob 758 relative to the crank to its off position connected between the switch cam 770 and the crank 768 is a leaf spring 794 as best seen in fig1 and 13 one end of the leaf spring 794 is connected using a small bolt 796 to the switch cam 770 the other end abuts a stop 798 on the crank 768 the leaf.