The frame base plate and {HEAD ~ the two frame end plates} together form {TAIL ~ a C shaped structure} 
together form
The frame base plate and { HEAD ~ the two frame end plates } together form { TAIL ~ a C shaped structure }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL