An apparatus for simultaneously forming a plurality of {HEAD ~ closely spaced, parallel grooves} having {TAIL ~ a web} between them in a thin walled tube is described 
having
An apparatus for simultaneously forming a plurality of { HEAD ~ closely spaced , parallel grooves } having { TAIL ~ a web } between them in a thin walled tube is described
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH