Rockwell Hardness Scale
The Industry Reference Standard
by Jeff Jackson, Mitchell Golf

Golf clubs may be constructed from various materials.  Among the most popular are 431 stainless steel, carbon steel and titanium.  Each of these metals, not to mention the number of other metals used in golf club manufacturing, have different properties.  One of the key properties used when discussing the metallurgy of a golf club head is hardness.  There are some players who claim to be able to tell if one club is softer than another, if one club can "work" the ball better than another and so on.  Whether they are actually feeling the metal in the head is debatable; what they are most likely feeling is a result of the club's particular head design.

In any event, there is a definitive measure of a metal's hardness.  The measure is known as the Rockwell Hardness Scale and uses an alpha-numeric designation to compare different metals.  The Rockwell Scale, developed in conjunction with the ASTM (American Society for Testing and Materials) is the most often used measure of metal hardness in the world today.  In a Rockwell test, a metal ball or cone with a known hardness is pressed into the metal being tested at a load of up to 100 kilograms.  At the point of deformation of, or penetration into, the metal being tested, the Rockwell Hardness is defined.  For example, aluminum deforms much more quickly than stainless steel.  Its Rockwell Hardness is in the B50-60 range, while stainless steel has a hardness in the mid-C range.  The higher the alpha-numeric designation, the harder the metal.  That is a "C is harder than a "B", a "30" is harder than a "20", etc.