| 摘要 |
A tennis racks having hollow strings is more solid than normal racket in string structure. It is necessary to displace air with oil to prevent reducing of elastic force caused by vacuum inside string. M.P. of the oil is above 30≦̸C and showing fluidity at above 50≦̸C such as petrolatum which is similar to CnH2m-2 cycle hydrocarbon. The string unit(1) is made by synthetic resin such as polyamide monofilament and hollow part(2) is filled up with the oil (3).
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