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

(ii) Woods and Irons

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:

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

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:

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

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.