Shafts are quantified in a number of different ways. The most common is the shaft flex. Simply, the shaft flex is the amount that the shaft will bend when placed under a load. A stiffer shaft will not flex as much, which requires more power to bend and "whip" through the ball properly (which results in higher club speed at impact for more distance), while a more flexible shaft will whip with less power required for better distance on slower swings, but may torque and over-flex if swung with too much power causing the head not to be square, resulting in lower accuracy. Most shaft makers offer a variety of flexes. The most common are: L (Lady), A (Soft Regular, Intermediate or Senior), R (Regular), S (Stiff), and X (Tour Stiff, Extra Stiff or Strong). A regular flex shaft is generally appropriate for those with an average head speed (80-94 mph), while an A-Flex (or senior shaft) is for players with a slower swing speed (70-79 mph), and the stiffer shafts, such as S-Flex and X-Flex (Stiff and Extra-Stiff shafts) are reserved only for those players with an above average swinging speed, usually above . Some companies also offer a "stiff-regular" or "firm" flex for players whose club speed falls in the upper range of a Regular shaft (90-100 mph), allowing golfers and clubmakers to fine-tune the flex for a stronger amateur-level player.