Doors or gates are provided to control the amount and {HEAD ~ width} of {TAIL ~ the discharge} of particulate material to the highway surface 
of
Doors or gates are provided to control the amount and { HEAD ~ width } of { TAIL ~ the discharge } of particulate material to the highway surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH