A golf club head comprising a body and a plurality of stiffening members, the tension or compression of which can be adjusted, is disclosed herein. The body comprises a face section, a sole section, and a crown section or a return section, and also defines a hollow interior. Each of the plurality of stiffening members is at least partially disposed within the hollow interior, and extends from the crown section or return section to the sole section to reduce stresses placed on the face during impact with a golf ball. The compression or tension of the stiffening members may be adjusted to affect the stresses experienced by the golf club head upon impact with a golf ball.

A method includes: determining a mass of a golf shaft having a length; determining a center of mass of the golf shaft; determining one or more characteristics of an insert based on: the mass of the golf shaft; and a target mass for golf shafts having the length; determining a location of the insert between a first end of the golf shaft where a golf grip is to be attached and a second end of the golf shaft where a golf club head is to be attached based on: the center of mass of the golf shaft; and a target center of mass for golf shafts having the length; and inserting an insert having the determined one or more characteristics within an interior of the golf shaft at the determined location, thereby creating an interference fit between the insert and the interior of the golf shaft.

A method includes: determining a mass of a golf shaft having a length; determining a center of mass of the golf shaft; determining one or more characteristics of an insert based on: the mass of the golf shaft; and a target mass for golf shafts having the length; determining a location of the insert between a first end of the golf shaft where a golf grip is to be attached and a second end of the golf shaft where a golf club head is to be attached based on: the center of mass of the golf shaft; and a target center of mass for golf shafts having the length; and inserting an insert having the determined one or more characteristics within an interior of the golf shaft at the determined location, thereby creating an interference fit between the insert and the interior of the golf shaft.

A test fixture for identifying the sweet spot of a bat suspends the bat in a vertical orientation via a fixed pivot point and limits rotational movement of the bat to a single plane. A pendulum with an impact mass is caused to contact the bat at various locations along the barrel of the bat at a fixed velocity. Rotational movement of the impact mass is limited to the single plane. Peak acceleration is measured proximate to the handle of the bat. The sweet spot is identified based on measured minimum peak acceleration. For example, if there is a single measured minimum peak acceleration then the corresponding contact location at the barrel is the sweet spot. If there are multiple measured minimum peak acceleration instances then a center or average contact location of those instances in identified as the sweet spot.

A test fixture for identifying the sweet spot of a bat suspends the bat in a vertical orientation via a fixed pivot point and limits rotational movement of the bat to a single plane. A pendulum with an impact mass is caused to contact the bat at various locations along the barrel of the bat at a fixed velocity. Rotational movement of the impact mass is limited to the single plane. Peak acceleration is measured proximate to the handle of the bat. The sweet spot is identified based on measured minimum peak acceleration. For example, if there is a single measured minimum peak acceleration then the corresponding contact location at the barrel is the sweet spot. If there are multiple measured minimum peak acceleration instances then a center or average contact location of those instances in identified as the sweet spot.

Examples of golf club heads and methods to manufacture golf club heads are generally described herein. In one example, a body portion of a golf club head may include a cavity having an opening and an internal structure defined by a wall portion and a base portion. A hosel portion may include an insert portion and a neck portion extending therefrom. The hosel portion may be attached to the body portion by an interference fit between the neck portion and the opening of the cavity. The insert portion may be received inside the cavity and may be spaced apart from the internal structure of the cavity. A space between the insert portion and the internal structure of the cavity may be partially or entirely filled with an adhesive to hold the hosel portion in place. Other examples may be described and claimed.

A golf club including at least one component with a construction that includes a composite material with color/metallic coated fibers. In some embodiments, at least a portion of an outer surface of the golf club head is defined by a layered structure including color/metallic coated fibers. The layered structure may include a non-woven composite layer comprising a plurality of unidirectional fiber composite plies and woven composite layer disposed over the non-woven fiber composite layer and including color/metallic coated fibers. In some embodiments, an optically transparent coating may be disposed over the woven composite layer. In some embodiments, the color/metallic coated fibers may be electroplated fibers.

A golf club including at least one component with a construction that includes a composite material with color/metallic coated fibers. In some embodiments, at least a portion of an outer surface of the golf club head is defined by a layered structure including color/metallic coated fibers. The layered structure may include a non-woven composite layer comprising a plurality of unidirectional fiber composite plies and woven composite layer disposed over the non-woven fiber composite layer and including color/metallic coated fibers. In some embodiments, an optically transparent coating may be disposed over the woven composite layer. In some embodiments, the color/metallic coated fibers may be electroplated fibers.

A golf club head and golf club having a lightweight non-metallic face insert bonded in an insert opening, large head dimensions, and large face characteristics, as well as unique mass property attributes driven by relationships not often considered in conventional club head design, to achieve a resistance to squaring the club head during a golf swing that is comfortable to the novice golfer, stability during off-center impacts, and preferred launch characteristics. This is achieved in part via establishing a club head configuration and associated center of gravity location that results in a preferred magnitude of Delta1 and Delta2 values, CG angle, moments of inertia, and associated ratios, relationships, and club head mass property characteristics influenced by these variables to achieve improved performance.

An object hardness measuring device includes a first side portion, a second side portion, a pedestal unit, a load unit, a measuring unit, and a holding unit. The load unit applies a load to the measurement object. The measuring unit is able to measure, in a state where the load acts on the measurement object, at least one of a movement distance of the second side portion with respect to the first side portion and a change amount of the load when the second side portion is moved either at a predetermined speed or to a predetermined position. The holding unit is able to hold the measurement object, and is movable between the first side portion and the second side portion by the slide rail unit.