| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve repulsion performance and flying distance, and make optimum thickness combination having sufficient durability for strength by making the thickness of an outer pipe ball hitting part of a double-pipe bat in a specified dimension range. SOLUTION: A double-pipe bat (softball bat) is fitted a reinforcing inner pipe 3 inside of an outer pipe 2 corresponding to a ball hitting part 2A, where the thickness of the ball hitting part 2A of the outer pipe 2 is 1.00-1.60 mm. Titanium, titanium alloy, aluminum alloy, or fiber-reinforced plastic can be used for material of the outer pipe 2. For example, in the case of an aluminum alloy bat, the outer pipe of the same material is integrally formed as a bat head 2B by preforming the outer pipe 2 having an opening at the bat head 2B through a swaging machine, inserting the inner pipe 3 from the opening to the part corresponding to the ball hitting part, and drawing the opening through spinning processing.</p> |
