A smoothly curved contact surface portion 121 disposed at {HEAD ~ the back side} near {TAIL ~ one end remote} from spring 13 and is forced into close contact with the surface of the smoothly arched notch 101 
near
A smoothly curved contact surface portion 121 disposed at { HEAD ~ the back side } near { TAIL ~ one end remote } from spring 13 and is forced into close contact with the surface of the smoothly arched notch 101
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH