Impact Area Roughness and Material
| Except for markings specified in the following paragraphs, the surface roughness within the area where impact is intended (the “impact area”) must not exceed that of decorative sandblasting, or of fine milling. The whole of the impact area must be of the same material (exceptions may be made for clubheads made of wood).
(i) Definition of “Impact Area”
For iron clubs, the "impact area" is deemed to be that part of the club where a face treatment has been applied (for instance grooves, sandblasting etc) or the central strip down the middle of the club face having a width of 1.68 inches (42.67mm), whichever is greater.
The impact area on driving clubs and fairway woods is deemed to be the central strip down the middle of the clubface having a width of 1.68 inches (42.67mm) – see Figure 34a.
NOTE: Grooves and/or punch marks indicating a traditional impact area (see Figure 34b), or any groove which encroaches into the heel or toe portions of the impact area by less than 0.25 inches (6.35mm), will not be considered to be within the impact area. However, any such markings must not be designed to unduly influence, or have the effect of unduly influencing, the movement of the ball.
Fig. 34 - Impact Area for Driving Clubs and Fairway Woods
For clubs with insets in the face, the boundary of the impact area is defined by the boundary of the inset, as long as any markings outside the boundary do not encroach the impact area by more than 0.25 inches (6.35mm) and/or are not designed to influence the movement of the ball.
Moreover, the inset itself must extend at least 0.84 inches (21.34mm) either side of the centre line of the face and to within at least 0.2 inches (5.08mm) of the top line and leading edge of the face.
The above definitions of the impact area only apply to new models of clubs manufactured on or after 1 January 2010. For clubs manufactured prior to 1 January 2010, please refer to the end of Supplementary Paper B.
(ii) Impact Area Roughness
When dealing with the surface roughness of a club face (not including putters, see Section 9 - Putter Face), the claims made by the manufacturer must be taken into account – especially if there is a claim that the roughness of the face influences the movement of the ball. In the absence of such claims, the ruling would be made purely on the amount of roughness there is. Sandblasting or other treatments of roughness greater than 180 micro inches (4.5 μmetre) are not permitted. In addition to this requirement for roughness, milling is not permitted if the crest to trough depth exceeds 0.001 inches (0.025mm). A reasonable tolerance is allowed for both of the above measurements. Non-conforming sandblasting or milling usually feels rough to the touch.
(iii) Impact Area Material
The requirement that the whole of the ‘impact area’ must be of the same material does not apply to clubs made of wood or putters (see Section 9 - Putter Face). The reason why it does not apply to wooden headed clubs is to allow the continued use of wooden clubs which have plastic insets and brass screws in the centre of the face. This design was commonly used in the old persimmon woods, some of which may still be in use. It is worth noting that a club face or inset made of a composite material would be considered to be of a single material and, therefore, would not be contrary to this Rule.
Metal wood club faces which have insets of different material not trapezoidal in shape may be permitted if the height of the inset meets the definition of the impact area and the width of the inset is the same as the height in at least one point. However, in order to preserve the intent of the "same material" Rule, clubs which have unusually shaped insets of different material (i.e. other than circular, oval, square or rectangular) would not normally be permitted.
If an inset of different material is permitted under the above guideline, the inset would be considered the ‘impact area’ for that club. Therefore, any markings outside that area need not conform to the specifications laid down in Appendix II, 5c. However, such markings must not be designed to unduly influence the movement of the ball.