M4 has the revolutionary Twist Face technology where the face corrects heel and toe contacts with a focus on the middle of the fairway, which produces straighter shots and more consistent distance. The Hammerhead track in the sole gives higher ball speed over a larger part of the face and removes unwanted spin. Geocoustic technology produces an explosive sound and allows for a larger and more forgiving face. What differentiates the M4 21 from the previous version is the graphic for the M4 logo on the club head and the head cover. Please note that the wrench tool is not included.