Preferably, {HEAD ~ the first housing} has a third engagement part to be engaged with {TAIL ~ the first mating part} 
Preferably , { HEAD ~ the first housing } has a third engagement part to be engaged with { TAIL ~ the first mating part }
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL