Each of the components, including the mirrors, anode, and cathode, must be sealed to {HEAD ~ the block} to form {TAIL ~ a gas tight seal} 
to form
Each of the components , including the mirrors , anode , and cathode , must be sealed to { HEAD ~ the block } to form { TAIL ~ a gas tight seal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL