The pivot mechanism 20 permits pivoting about a vertical axis, and permits {HEAD ~ limited relative motion} between {TAIL ~ the front and rear frame sections} 16 and 18 about a horizontal axis 
The pivot mechanism 20 permits pivoting about a vertical axis , and permits { HEAD ~ limited relative motion } between { TAIL ~ the front and rear frame sections } 16 and 18 about a horizontal axis
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH