4. Clubhead

a. Plain in Shape

The clubhead must be generally plain in shape. All parts must be rigid, structural in nature and functional. The clubhead or its parts must not be designed to resemble any other object.

It is not practicable to define plain in shape precisely and comprehensively. However, features that are deemed to be in breach of this requirement and are therefore not permitted include, but are not limited to:

(i) All Clubs

• holes through the face;

• holes through the head (some exceptions may be made for putters and cavity back irons);

• features that are for the purpose of meeting dimensional specifications;

• features that extend into or ahead of the face;

• features that extend significantly above the top line of the head;

• furrows in or runners on the head that extend into the face (some exceptions may be made for putters); and

• optical or electronic devices.

(ii) Woods and Irons

• all features listed in (i) above;

• cavities in the outline of the heel and/or the toe of the head that can be viewed from above;

• severe or multiple cavities in the outline of the back of the head that can be viewed from above;

• transparent material added to the head with the intention of rendering conforming a feature that is not otherwise permitted; and

• features that extend beyond the outline of the head when viewed from above.

b. Dimensions, Volume and Moment of Inertia

(i) Woods

Dimensional specifications:

When the club is in a 60 degree lie angle, the dimensions of the clubhead must be such that:

• the distance from the heel to the toe of the clubhead is greater than the distance from the face to the back;

• the distance from the heel to the toe of the clubhead is not greater than 5 inches (127 mm); and

• the distance from the sole to the crown of the clubhead, including any permitted features, is not greater than 2.8 inches (71.12 mm).

These dimensions are measured on horizontal lines between vertical projections of the outermost points of:

• the heel and the toe; and

• the face and the back (see Fig. 42, dimension A); and on vertical lines between the horizontal projections of the outermost points of the sole and the crown (see Fig. 42, dimension B). If the outermost point of the heel is not clearly defined, it is deemed to be 0.875 inches (22.23 mm) above the horizontal plane on which the club is lying (see Fig. 42, dimension C).

Volume limit:

The volume of the clubhead must not exceed 460 cubic centimetres (28.06 cubic inches), plus a tolerance of 10 cubic centimetres (0.61 cubic inches).

Moment of Inertia (MOI):

When the club is in a 60 degree lie angle, the moment of inertia component around the vertical axis through the clubhead’s centre of gravity must not exceed 5900 g cm2 (32.259 oz in2), plus a test tolerance of 100 g cm2 (0.547 oz in2).

(ii) Irons

When the clubhead is in its normal address position, the dimensions of the head must be such that the distance from the heel to the toe is greater than the distance from the face to the back.

(iii) Putters (see Fig. 44)

When the clubhead is in its normal address position, the dimensions of the head must be such that:

• the distance from the heel to the toe is greater than the distance from the face to the back;

• the distance from the heel to the toe of the head is less than or equal to 7 inches (177.8 mm);

• the distance from the heel to the toe of the face is greater than or equal to two thirds of the distance from the face to the back of the head;

• the distance from the heel to the toe of the face is greater than or equal to half of the distance from the heel to the toe of the head; and

• the distance from the sole to the top of the head, including any permitted features, is less than or equal to 2.5 inches (63.5 mm).

For traditionally shaped heads, these dimensions will be measured on horizontal lines between vertical projections of the outermost points of:

• the heel and the toe of the head;

• the heel and the toe of the face; and

• the face and the back;

and on vertical lines between the horizontal projections of the outermost points of the sole and the top of the head.

For unusually shaped heads, the toe to heel dimension may be made at the face.

c. Spring Effect and Dynamic Properties

The design, material and/or construction of, or any treatment to, the clubhead (which includes the club face) must not:

(i) have the effect of a spring which exceeds the limit set forth in the Pendulum Test Protocol on file with The R&A and USGA; or

(ii) incorporate features or technology including, but not limited to, separate springs or spring features, that have the intent of, or the effect of, unduly influencing the clubhead’s spring effect; or

(iii) unduly influence the movement of the ball.

Note: (i) above does not apply to putters.

d. Striking Faces

The clubhead must have only one striking face, except that a putter may have two such faces if their characteristics are the same, and they are opposite each other.