It will also depend on the ply in addition to the weight. For example, you will need a bigger eye for a 60/3 than a 60/2 thread. I test the thread with the needle. Put the needle on a length of thread and hold it up at a 45 degree angle. Does the needle move? If it does not, go to a bigger needle. Does it fly down the length? If so, go to a smaller needle. The needle should "hop" down the thread. If it does, you have the right size.