tennis ball with elastic string and computer string it can use ... area,making tension test Tension force:custom. Item nameTennis ball with elastic string and computer stringMaterialPolyster/LatexDiameter0.45mm-0.5mm ... ; Spandex, as per the client's request Rubber/Latex 23#,28#,32#,37#,42#,52#,63#,90#,100#, Spandex 420D ... a opp,and many tube in a carton tennis ball with elastic string and computer string