The key 1320 is sleeved on the recessed portion 1312, and {HEAD ~ a surface} 1322 of {TAIL ~ the key} 1320 is more depressed than the protrusion portions 1314 
of
The key 1320 is sleeved on the recessed portion 1312 , and { HEAD ~ a surface } 1322 of { TAIL ~ the key } 1320 is more depressed than the protrusion portions 1314
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH