... tension test Tension force:custom. Item nameTennis ball with elastic string and computer stringMaterialPolyster/LatexDiameter0.45mm-0.5mm ColorBlack (we ... . Cotton 20/1, 20/2, 20/3, 30/1, 30/2, 30/3, 40/1, 40/2, 40/3, 50/1, ... 50/2, 50/3 etc Nylon ... Packing method 1 tube insert a opp,and many tube in a carton tennis ball with elastic string and computer string