{HEAD ~ The casing} 30 and the collar 40 also form {TAIL ~ a smooth and curved outer shape} so as to reduce the turbulence 
form
{ HEAD ~ The casing } 30 and the collar 40 also form { TAIL ~ a smooth and curved outer shape } so as to reduce the turbulence
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH