for what type of fly?? - I think you may be refering to the zonker - never tied one, but understand you use zonker-tape, or magnetic peel and stick sheet, cut in the shape you want and stick the two halves together over the hook somehow, slide you mylar tubing over it and you are on your way. do a search for zonker fly patterns.
amy ruiz on ebay who gos by vintageflies sells everything for tube flies, mylar tubing in awesome colors, tube flie bodies real cheap and a tube flie vise, everything for under 30 dollars my bill came to. totally reccomend it if you like mylar or tube flies
saltwater flyfishing in the northwest is a science as well as an art