The new MB (Muscle Back) irons maintain the classic lines, profile, solid sound, feel and shot-shaping precision of classic forgings. However, they also provide modern playability, a benefit resulting from more than thirty years of player research and development, engineering innovation and advances in manufacturing processes. The MB irons feature a redesigned back and faceted surface known as the "dog bone." This surface is larger in the heel and toe while narrowing behind the impact area. This allocates more mass behind the impact area for the traditional solid feel expected from blade irons.