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