There are a few clubhead design parameters that affect the direction and trajectory one hits a golf ball. These terms are face progression, offset and onset, which are either foreign to the average golfer or at least confusing at best. Lets help sort out these terms as they are all related to one another by first starting out by established a point of reference which is the centerline axis of the shaft indicated by the red line in Figure 1.
Golf clubs are measured by foundries and golf club manufacturers using heavy duty industrial specification gauges. The base of a specs (for short) gauge has a series of lines engraved, one of which shows how the vertical centerline of the shaft translates to the horizontal plane as a means of referencing many things about a golf club. One of these is face progression which is simply the measurement from a shafts centerline to the leading edge of the club face. In Figure 2, the leading edge of the face is indicated by the green line. The difference between the red and green lines is the face progression.
Face progression is usually a term that is related to woods, but can be used for irons, wedges, hybrids and putters too. On a wood, the leading edge is forward of the centerline axis of the shaft. For irons, wedges and hybrids the leading edge may be in front of, behind or even with the centerline axis of the shaft, so there are positive and negative values associated with face progression. For our reference, when the leading edge is forward of the centerline axis of the shaft, this will be a positive value.