You can thread a 2 mm ring on a leader made from 4 lb mono? WOW! That has got to be a tight fit. I use NICHE rings and the 2 mm is the size of a #10 fly hook eye. I do use them on the Kathy Scott leaders and they are perfect. For my 5 1/2' and 6' with 14/12/10/8/6 I use the NICHE 3 mm. I do know that each company's rings are a little different. I was using Streamside, but have recently switched