Abstract: A tapered hollow shaft made of a fiber reinforced composite material, which comprises: (a) at least one angle layer consisting essentially of polyacrylonitrile-based carbon fibers having a tensile modulus ranging from 200 to 500 GPa and a tensile strength ranging from 4000 to 5600 MPa; (b) at least one straight layer consisting essentially of polyacrylonitrile-based carbon fibers having a tensile modulus ranging from 200 to 460 GPa and a tensile strength ranging from 3500 to 5600 MPa; (c) at least one reinforcing layer consisting essentially of pitch-based carbon fibers or polyacrylonitrile-based carbon fibers each having a compressive breaking strain of 1.7 to 5.0%, a tensile modulus ranging from 5 to 160 GPa, a tensile strength ranging from 500 to 3000 MPa and a density ranging from 1.5 to 1.

Abstract: A pitch-based carbon fiber reinforced composite material is improved with regard to its compressive strength and compression strain at failure by combining polyacrylonitrile-based carbon fibers. The pitch-based carbon fibers have a modulus in tension of not less than 400 GPa, a tensile strength of not less than 2000 MPa, a compressive strength as a unidirectionally reinforced composite material of 100 MPa to 800 MPa and a fiber diameter of 4 .mu.m to 15 .mu.m and the polyacrylonitrile-based carbon fibers have a modulus in tension of not less than 200 GPa, a compressive strength and compression strain at failure as a unidirectionally reinforced composite material larger than those of the pitch-based carbon fibers, and a fiber diameter smaller than that of the pitch-based carbon fibers.

Abstract: An aqueous emulsion type sizing agent for carbon fibers is disclosed. The sizing agent contains a compound represented by the following general formula (I): ##STR1## wherein A represents (C.sub.2 H.sub.4 O).sub.l or (C.sub.2 H.sub.4 O).sub.n (C.sub.3 H.sub.6 O).sub.m [l is 18 to 70; n is 18 to 70; and m is 2 to 50 (1.ltoreq.n/m.ltoreq.35)];a compound represented by the following general formula (II): ##STR2## wherein R represents C.sub.q H.sub.2q+1 or ##STR3## (q is 10 to 18; and p is 15 to 70); and an epoxy resin, a process for preparation of the agent, and the method for using it are also disclosed. The sizing agent has excellent emulsion stability and heat stability, and it can impart excellent bundling properties to carbon fibers.