| 摘要 |
PROBLEM TO BE SOLVED: To securely hold a heavy bowl in a relaxed state by hooking the inside of thumb in the thumb hole by arranging a fixing means of thumb in the thumb hole opened on the surface of a bowling ball. SOLUTION: A fixing means 10 by which the inside B of a thumb A can be fixed, is fitted in a thumb hole 1 formed on the surface of a bowling ball 1. As the fixing means 10, a lateral hole 11 is formed for instance, in which the thumb can be inserted when the joint of thumb A is bent to the inside B. Or a fold is formed, in which the thumb is caught in the fold when the joint of the thumb is bent to the inside. A cutting tool to form a lateral hole 11 in the thumb hole 2 is constituted of a a file a little thinner than the inside diameter of the thumb hole 2 and the shaft thinner than the diameter of the file. The end of the shaft is connected to an electric drill or the jaw of a boring machine and the file is inserted in the thumb hole 2 of the ball 1 and pushed to the part to be required to cut while rotating the file to obtain the lateral hole 11. |
