will be more fully explained below shaft 2 is typically fabricated of two different materials the first material is a high strength and high modulus set of fibers for example graphite glass or boron the second material is a matrix or adhesive for example epoxy plastic resin or a phenolic the composite material can be such as to cure in stages it is sometimes fabricated in an uncured or partially cured form in the form of a tape having a single row of fibers aligned parallel to each other embedded in the matrix material in this form it is referred to as a pre impregnated tape or pre preg fig2 is a side view of one embodiment of a double sleeve structure 7 the sleeves have been machined in joined quantities of two to facilitate mass production they will later be severed along the line illustrated near the point of joinder the sleeves are free of grooves however subsurface channels or grooves 6 occupy a large portion of the surface area of double sleeve 7 the grooves are aligned parallel to each other are closely spaced and have a radius of approximately one to four times that of the fibers employed in composite shaft 2 in the embodiment.