Putting is the most precise aspect of the game of golf. The putter must be designed to give the golfer every technical advantage including smooth stroke, good glide, sweet impact, and bounce-less topspin ball launch as well as every technique advantage including perfect fit as to shaft angle and length.
Putters usually have a loft of 5° but cannot be more than 10°. The putter is the only club that may have a grip that is not perfectly round; "shield"-like cross-sections with a flat top and curved underside are most common. The putter is also the only club allowed to have a bent shaft; often, clubmakers will attach the shaft to the clubhead on the near edge for visibility, but to increase stability, the shaft is bent near the clubhead mounting so that its lie and the resulting clubhead position places the line of the straight part of the shaft at the sweet spot, where the ball should be for the best putt. This increases accuracy as the golfer can direct their swing through the ball, without feeling like they are slightly behind it.
The design of the putter's clubhead has undergone radical change in the last 20–30 years, as have many club types. The putter was originally a forged iron piece very similar in shape to the irons of the day. Through attempts to lower the center of gravity of the clubhead, it evolved into a shorter, thicker head slightly curved from front to rear (the so-called "hot dog" putter). The introduction of investment casting for club heads allowed drastically different shapes to be made far more easily and cheaply than with forging, resulting in several design improvements. First of all, the majority of mass behind the clubface was placed as low as possible, resulting in an L-shaped side profile with a thin, flat clubface and another thin block along the bottom of the club behind the face. Additionally, peripheral weighting, or the placing of mass as far away from the center of the clubface as possible, increases the moment of inertia of the clubhead, reducing twisting if the club contacts the ball slightly off-center and thus giving the club a larger "sweet spot" with which to contact the ball. Newer innovations include replacing the metal at the "sweet spot" with a softer polymer compound that will give and rebound at impact, which increases the peak impulse (force per millisecond) imparted to the ball for better distance. Putters are subdivided into mallet, peripheral weighted and blade styles. Power adjustability and practice/play convertibility are features embodied in the latest putter design technology.
