Abstract: Three cylindrical concaves (reduced thickness portions) are formed in the intermediate portion between the centering so as to be spaced apart each other in the direction of the axis of the shaft inserting hole. The cylindrical concaves are formed to have an inner diameter of 11.3 mm that is larger than the inner diameter at the centering portions by removing the thickness of the hosel portion from its inner diameter of the centering portions towards outer side. The summed lengths of the bottom surfaces (peripheral surfaces) of the cylindrical concaves in the direction of the axis of the shaft inserting hole is 12 mm, thus reducing weight of the hosel portion by 3.03 g compared with conventional hosel portions. The reduced weight can be reallocated, to the sole portion. The gold thus produced in less expensive and has a reduced weight of the hosel.

Abstract: In order to sharpen and harden a corner portion of a score line edge portion of an iron golf club having a plurality of score lines on a face surface within a prescribed range, heat input is implemented on an edge portion of a groove through laser irradiation after the groove is machined and, as a result, the edge portion is hardened and melted to form a rounded corner R. The hardness is set at a Vickers hardness value (HV) of at least 350. The corner R forms a part of a contour line of the edge portion and this contour line is formed to exist between a first circle that contacts the face surface and a side surface of the groove and has a radius of 0.010 inches (0.254 millimeters) and a second circle that is concentric with the first circle and has a radius of 0.011 inches (0.2794 millimeters).

Abstract: The present invention provides a golf club improved in ball hitting sound and ball hitting feeling and its manufacturing method. First, low-carbon steel is subjected to press processing of hot forging to form portions of irregularity on the face on a side of a hitting surface. Then, when there are projecting portions in the portions of irregularity, only the projecting portions are subjected to press processing of cold forging to crush the projecting portions to be flat. Then, the surface is slightly smoothed by machining to be flat and crystal grains at the portions of irregularity and the area therearound are pressed to be fined, thereby enhancing the hardness and forming fiber flows parallel to the hitting surface. A part of the hardened face becomes harder than the hardness of a base material before press processing by 10% or more within a range of 1 mm in a depth.

Abstract: There is provided a golf club head capable of reliably preventing a backspin rate from varying in rainfall. A plurality of fine grooves are formed on a face surface 2. When observing a cross-sectional surface perpendicular to the face surface 2 involving a vertical line passing through the center G of gravity of the golf club head 1 with the golf club head 1 set at preset loft and lie angles, an average width of the fine grooves 4 in the cross-sectional surface is 100 ?m or less and an average pitch thereof in the cross-sectional surface is 100 ?m or less. Hence, the discharge of water can be accelerated by a capillary phenomenon, making it possible to reliably prevent a backspin rate of a golf ball from varying in rainfall.

Abstract: Three cylindrical concaves (reduced thickness portions) are formed in the intermediate portion between the centering so as to be spaced apart each other in the direction of the axis of the shaft inserting hole. The cylindrical concaves are formed to have an inner diameter of 11.3 mm that is larger than the inner diameter at the centering portions by removing the thickness of the hosel portion from its inner diameter of the centering portions towards outer side. The summed lengths of the bottom surfaces (peripheral surfaces) of the cylindrical concaves in the direction of the axis of the shaft inserting hole is 12 mm, thus reducing weight of the hosel portion by 3.03 g compared with conventional hosel portions. The reduced weight can be reallocated, to the sole portion. The gold thus produced in less expensive and has a reduced weight of the hosel.

Abstract: In order to sharpen and harden a corner portion of a score line edge portion of an iron golf club having a plurality of score lines on a face surface within a prescribed range, heat input is implemented on an edge portion of a groove through laser irradiation after the groove is machined and, as a result, the edge portion is hardened and melted to form a rounded corner R. The hardness is set at a Vickers hardness value (HV) of at least 350. The corner R forms a part of a contour line of the edge portion and this contour line is formed to exist between a first circle that contacts the face surface and a side surface of the groove and has a radius of 0.010 inches (0.254 millimeters) and a second circle that is concentric with the first circle and has a radius of 0.011 inches (0.2794 millimeters).

Abstract: A gold club in which the repulsion area of the face portion is shifted downward, and a manufacturing method of such a golf club are provided. The structure of the golf club is such that, in order to shift the sweet area of a face portion having a striking face downward, a crown portion is subjected to an age hardening process to intentionally enhance any one or more of the mechanical qualities of material of the rigidity, strength and hardness of the crown portion. By shifting the sweet area downward, eventually a repulsion effect in the shifted position can be improved, and a ball can be struck without causing a decrease in a traveling distance as in the case when striking the ball on the upper position, even if the striking position is the position shifted to the lower part of the face portion.

Abstract: A first crystalline polypropylene of the present invention satisfies the relationships of the following formulae (1) and (2): &agr;≦−0.42×ln(Mp)+7.3  (1),and Tm>1.85×ln(Mp)+144.5  (2), wherein &agr; is a 0° C. soluble content (% by weight) as measured through programmed-temperature fractionation, Mp is a peak molecular weight in a molecular weight distribution curve as measured through gel permeation chromatography, and Tm is a melting point (° C.) as measured through differential scanning calorimetry. A second crystalline polypropylene of the present invention satisfies the relationship given in the following formula (3): &agr;≦1.11[&eegr;]−0.42+1.40  (3) wherein &agr; is the same as above and [&eegr;] an intrinsic viscosity (dl/g) as measured in a tetralin solvent at 135° C.

Abstract: A first crystalline polypropylene of the present invention satisfies the relationships of the following formulae (1) and (2):

Abstract: The present invention relates to a process for producing a stretched molding which comprises stretching a straight chain random copolymer having:a repeating unit (A) represented by the formula:--CH.sub.2 --CH.sub.2 --and a repeating unit (B) represented by the formula: ##STR1## the proportion of said repeating unit (B) being 0.01 to 10 mol %; and an intrinsic viscosity [.eta.] as measured at 135.degree. C. in decalin of at least 5 dl/g.A stretched molding obtained by the present invention has mechanical properties equivalent or superior to those of the conventional super high molecular weight polyethylene stretched molding and is excellent in adhesive properties, dyeability, printability and so on, and thus is greatly useful as an industrial material required to have high strength and further good adhesive properties and printability.