Abstract: A golf club head with a hollow therein includes a face portion and a main body portion including a crown portion and a sole portion extending rearward from the face portion. The main body portion is provided with a slit penetrating the main body portion to the hollow, and a surrounding area of the slit is at least partially provided with a thick portion. The slit is arranged so that at least part of the slit is visible in a front view of the golf club head under its reference state, where the reference state is such that the head is placed on a horizontal plane at a lie angle and a loft angle specified for the head, while keeping a shaft axis center line of the head on a reference vertical plane.

Abstract: A golf club head with a hollow therein comprises a face portion and a main body portion including a crown portion and a sole portion extending rearward from the face portion. The main body portion is provided with at least one slit penetrating through the main body portion. The slit has a width in the toe-heel direction and a length in the front-rear direction which is larger than the width. The surrounding area of the slit is at least partially provided with a thick portion.

Abstract: A golf club head having a hollow portion therein, the head includes a main body including a crown portion and a sole portion, and a face member forming at least a part of a striking face for striking a ball. The main body is made of a first material having a first specific gravity. The face member is formed of a second material having a second specific gravity smaller than the first specific gravity. The main body is provided with at least one slit that penetrates the main body, and the at least one slit extends in a head-front-back direction.

Abstract: A golf club head having a hollow portion therein, the head includes a face portion, and a main body including a crown portion and a sole portion each extending backwardly from the face portion. The main body is provided with at least one slit that penetrates the main body and extends in a head-front-back direction. The at least one slit includes a pair of slit inner walls extending in the head-front-back direction and at least one joint connecting the pair of slit inner walls to each other.

Abstract: A golf club head with a hollow therein comprises a face portion and a main body portion including a crown portion and a sole portion extending rearward from the face portion. The main body portion is provided with at least one slit penetrating through the main body portion. The slit has a width in the toe-heel direction and a length in the front-rear direction which is larger than the width. The surrounding area of the slit is at least partially provided with a thick portion.

Abstract: A golf club head having a cavity therein comprises a wall at least a part of which is formed as a convexo-concave wall portion. The convexo-concave wall portion is composed of convexed portions repeatedly arranged in a first direction and a second direction intersecting the first direction, and concaved portions formed between the convexed portions. Each of the convexed portions includes at least one first protrusion extending in the first direction and at least one second protrusion extending in the second direction.

Abstract: A golf club head having a cavity therein comprises a wall at least a part of which is formed as a convexo-concave wall portion. The convexo-concave wall portion is composed of convexed portions repeatedly arranged in a first direction and a second direction intersecting the first direction, and concaved portions formed between the convexed portions. Each of the convexed portions includes at least one first protrusion extending in the first direction and at least one second protrusion extending in the second direction.

Abstract: A method of forming a coating film includes dropping a first chemical onto a substrate to be treated and rotating the substrate, thereby forming a first coating film, the first chemical being comprised of a solvent and a solid added to the solvent, baking the first coating film, dropping a second chemical onto a first-chemical poorly-coated region of the stationary substrate, thereby forming a second coating film, the second chemical being comprised of a solvent and a solid added to the solvent, drying the second coating film, and baking the second coating film.