each said lock rod has {HEAD ~ a rib portion} extending across the upper end thereof for engagement with {TAIL ~ said blocking device} 
each said lock rod has { HEAD ~ a rib portion } extending across the upper end thereof for engagement with { TAIL ~ said blocking device }
OTH OTH OTH 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