Boom 16 has {HEAD ~ first and second arms} 20, 22 wherein {TAIL ~ second arm} 22 is shorter than first arm 20 
Boom 16 has { HEAD ~ first and second arms } 20 , 22 wherein { TAIL ~ second arm } 22 is shorter than first arm 20
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH