Guidance on How to Measure Grooves on Club Faces
for Conformance to the 2008-2009 Rules of Golf - In The Field
The following pages give guidance on how to measure grooves on club faces for width and separation, using the “Ink and Scratch” method, and depth. They concentrate solely on the Rules which apply to the grooves on iron and wood clubs available prior to January 1, 2010, but, if necessary, the same procedures and equipment can be used to measure grooves on a putter face (see Design of Clubs, Section 5f).
For those officials who have not previously carried out these measurements, we recommend setting aside time, a day or more prior to the tournament, for groove checking if required, rather than performing checks on the first day. It only takes a few minutes to measure the grooves on a club, but it is important not to be rushed. We also recommend practice-measuring on at least six club faces — preferably more — before performing it in the field.
A one-page summary of the procedure for measuring the width and separation of the grooves on iron and wood clubs is attached, which, when used in conjunction with the specially designed results sheet, may give sufficient instruction, once the user has gained some experience in measuring grooves. An abbreviated form of the test, appropriate for clubs which comfortably meet the groove specifications, is also outlined.
Groove Width and Separation
In order to carry out the “Ink and Scratch” method of measuring grooves, the following equipment is required:
- A thick black marker pen (e.g., a Sharpie®)
- A carbide wedge ‘Marking Tool’ (see Fig. 2)
- A magnifier
- A steel ruler
- An alcohol wipe (to clean the club face)
The carbide tool and magnifier are available from the USGA at a reasonable cost.
How to Ink and Mark the Grooves
1. Make sure that the club face and grooves are clean. Also check that the tungsten carbide “wedge” in the marking tool is properly square to the axis of the tool and securely fixed. If not, adjust with the Allen key provided.
2. Use the marker pen to coat an approximately 0.25 to 0.5 inch width of the edges of five grooves (and the nearby part of the flat area between them), making sure that the ink gets down into the grooves. The inked pattern thus formed should lie in a line running from the sole to top edge of the fifth groove. For new clubs, do this about 0.5 inches to one side of the center of the face (see Fig. 1 below). For used clubs, do it near the toe, but not at the very end of the grooves (but see also Supplement A, Paragraph 13).
3. When the ink is dry, take the marking tool, hold it like a pencil at about 45 degrees to the club face and insert the pointed corner of its tip into one of the blackened grooves (See Fig. 2). Using firm but not too heavy pressure, pull the tool along the groove for about 0.25 inches. Two narrow bright lines of exposed metal should now be visible, one on each side of the groove denoting the position of the edges of the grooves. (See Fig. 3).
Do the same for all five blackened grooves.
How to Use the Magnifier
4. The magnifier comes with two scales, a short scale with a line pre-measured at 0.035 inches (width scale) and a long scale (separation scale).
5. Rest the clubhead on a table or other surface, so that the club face is horizontal. You may find it helps to rest the club’s shaft on your shoulder or on some raised object, in order to leave both hands free to adjust the magnifier. Since good light is needed, it is helpful, indoors, to place a reading lamp close to the clubhead, preferably shining along the direction of the grooves on the club face. Make sure you hold the magnifier in such a way that your fingers do not obscure the light.
6. Place the magnifier on the club face and look through it. By turning the knurled ring on the eyepiece, you should be able to bring into sharp focus both the scale and surface features on the club face. You should also be able to see clearly the bright edges you have scraped on the grooves against the black background.
Notice that the magnifier scale is in thousandths of inches and is marked at intervals of 0.005 inches. (See Fig. 4).
Measuring the Grooves
7. Use the magnifier to measure the width (W) of the five grooves whose edges have been marked by the tool. This may be done by lining up the width scale along the left edge of each groove (i.e., along the left of the bright line scratched by the tool) and reading off the position of the other edge on the portion of the magnifier scale (i.e., along the left of the bright line scratched by the tool). For best results, the scratched line should be about 0.005 inches wide. If it is appreciably wider than 0.005 inches, then too much pressure has been applied in using the marking tool. In that case, abandon that particular part of the groove and do a repeat “ink and scratch” slightly to one side.
Record all five groove widths. Often they will be the same, or differ by only .0025 inches. Please refer to Supplement B of this Guide.
8. Determine the groove separation (D) (See Fig. 5).
Using the magnifier, measure the distance from one edge of groove 1 to the corresponding edge of groove 5 (i.e., over four land areas). The best way to do this is to position the separation scale on the left edge of groove 1 and read off the distance on the left edge of groove 5 (record as D on the worksheet).
Finally, determine the land area between the grooves (the distance between edges of adjacent grooves) by lining up the long magnifier along the right edge of one groove and the left edge of the next and reading off the position of the left edge of the groove.
Errors and Uncertainty in Measuring
9. With a little practice you can measure the groove width with as little as 0.0025 inch tolerance (i.e., it could be wrong by at most 0.0025 inches). In tests for conformity, the manufacturer is given the benefit of all of the uncertainty.
How to Determine Whether Grooves Conform to Pre-2010 Groove Requirements
Note: For most levels of play, clubs available prior to January 1, 2010 that conform to the pre-2010 requirements may continue to be used in rounds played under USGA Rules of Golf until at least 2024.
Definition of Impact Area for Clubs Available Prior to January 1, 2010
For iron clubs, the “impact area” is deemed to be that part of the face which lies within 0.80 inches (20 mm) on either side of the vertical center line of the face.
For metal wood clubs, the shape of the impact area is generally based on the traditional inserts used in persimmon-type wood clubs. The shape and dimensions of this area can best be illustrated as follows:
The height (h) of the trapezoid is used to fix the horizontal dimensions — namely “1/2h” at the top and “h” at the base. This ensures that all impact areas are similar (see Fig. 6).
10. The pre-2010 specifications for grooves that may be applied to the club face provide:
- Grooves must not have sharp edges or raised lips (test on file).
- Grooves must be straight and parallel.
- Grooves must have a symmetrical cross-section and have sides which do not converge.
- The width, spacing and cross-section of the grooves must be consistent throughout the impact area.
- Any rounding of groove edges shall be in the form of a radius which does not exceed 0.020 inches (0.508 mm).
- The width of the grooves shall not exceed 0.035 inches (0.9 mm), using the 30 degree method of measurement on file with the USGA.
- The distance between edges of adjacent grooves must not be less than three times the width of a groove, and not less than 0.075 inches (1.905 mm).
The specifications can be further explained as follows:
(i) The width must not exceed 0.035 inches (0.9 mm): We currently interpret “width” as the average width and, therefore, the measured grooves do not conform if the average width of grooves 1 through 5 is greater than 0.035 inches.
However, if any one groove is greater than the maximum allowable plus 0.002 inches, the club does not conform.
(ii) The distance between edges of adjacent grooves must be not less than three times the width of a groove. Using the average of the five groove widths, multiply it by three and compare it to your measurements of land area.
(iii) The distance between edges of adjacent grooves must not be less than 0.075 inches (1.9 mm): Again, using the average of the five groove widths, compare it to your measurements of land area (applies if the average groove width < 0.025 inches).
(iv) Groove widths must be consistent: We interpret this to mean that the difference in width between the second widest and the second narrowest groove must not exceed 0.005 inches.
11. We recognize that groove measurements made, as these are, at one point along the length of the grooves, are sensitive to small manufacturing errors. Therefore, if a club fails on one of the above criteria, it should not immediately be declared non-conforming; rather the whole measuring procedure should be repeated at a slightly different part of the face (perhaps 0.40 inches to the other side of the center of a club face from the first set). For a club to be declared non-conforming in the field, it must fail to meet the same specification on both sets of measurements. In the case of a single overwidth groove (Wmax), the same groove must be overwidth on both measurements.
Irregular or Unusual Grooves
12. For grooves with markedly varying separation (see Fig. 7), the same measuring technique applies. Difficult cases should be submitted to the USGA for a ruling.
13. For used clubs with worn grooves, the width measurements must be made on grooves which are not worn. These can nearly always be found near the toe of the club, or high on the face. Avoid the extreme end of the grooves since the width sometimes varies there. If it is not possible to find five unworn grooves, measure as many as possible and make the necessary modifications to the calculation of average width.
If the grooves on a used club have been deliberately altered by filing or the use of a groove scoring tool, then the club should be treated as though it were new and the grooves measured near the center of the face (see Rule 4-1b).
14. Very occasionally grooves will be found which are either very shallow, or have sides which make an angle of less than 30 degrees to the horizontal. In these circumstances the marking tool will not work properly and the club should be submitted to the USGA for a ruling, although if the grooves clearly conform, it may be possible to give a conforming ruling in the field.