Patent ID: 8012036

Claim:
A set of iron-type golf clubs comprising “n” pieces of iron-type golf clubs having club heads with different loft angles wherein “n” is an integer of 3 or more, each of the club heads having a ball-hitting face provided with a plurality of face grooves extending in a club head's toe-heel direction and having a depth of 0.200 to 0.508 mm and a plurality of auxiliary grooves having a depth of 0.005 to 0.025 mm, the auxiliary grooves including a plurality of first auxiliary grooves extending, in a vertically-placed face state that a club head is placed on a horizontal plane at prescribed line and loft angles given to the club head and is then tilted forward up to a loft angle of 0°, in at least a region between a toe side line extending at right angles to the face grooves with passing at toe side ends of the face grooves and a heel side line extending at right angles to the face grooves with passing at heel side ends of the face grooves, each of the first auxiliary grooves being formed, in said region, into a curved groove convex upward such that a curve descends from a peak toward both the toe side line and the heel side line, and an average degree of curvature θi calculated according to the following equation (1) of the first auxiliary grooves of each of the club heads satisfying the following equations (2) and (3): θ i =Σ{( H 1 j−H 2 j )/ W}/m ( j= 1 to m ) (1) θ1<θn (2) θ1≦θ2≦ . . . ≦θn (3) wherein: H 1 j is a height of the peak of a j-th first auxiliary groove from the horizontal plane, H 2 j is an average value between a height H 2 aj from the horizontal plane of an intersection point of the j-th first auxiliary groove with the toe side line and a height H 2 bj from the horizontal plane of an intersection point of the j-th first auxiliary groove with the heel side line, i.e., H 2 j =(H 2 aj +H 2 bj )/2, W is a horizontal distance between the toe side line and the heel side line, “m” is a total number of the first auxiliary grooves included in each of the club heads, and θi is an average degree of curvature of the first auxiliary grooves of each of the club heads, and the suffix “i” is an integer of 1 to “n” given to the club heads in order of loft angle from a club head having the smallest loft angle, in which “n” is a total number of the golf clubs included in the golf club set.