Japanese line size number 1 is .165mm. Sunline size 1 line is rated at 4lb. Varivas Master Spec fluorocarbon tippet that is .165mm is described as 4X and is rated at 5.1 lb. Their 3X is size 1.5 and is rated at 7.2lb. Varivas 2X is size 2 and is rated at 9.6 lb. 1X is size 2.5 and is 11.2 lb.