| 摘要 |
Before the ball is bowled, the pistons (1) are pushed into the sleeve (2) as far as a pressure release groove (8), the pistons becoming wedged. Now the bowling ball is bowled. As a result of centrifugal force, the action of a lifting spring (7) and the vibration arising on impact with the alley, the pistons fly up and engage. The piston surfaces now fill the gaps left by the grip holes, to the advantage of the true running and accuracy of a bowling or skittle ball. <IMAGE>
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