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