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