The force of the tumbler spring then pivots the tumbler into {TAIL ~ its assembled position} where the detent is engaged with {HEAD ~ the retaining ledge} 
The force of the tumbler spring then pivots the tumbler into { TAIL ~ its assembled position } where the detent is engaged with { HEAD ~ the retaining ledge }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD