I've used the head cement available for tying flies with good results but found the cost to be a little high due to the number of bottles I'd go through and so I started to experiment. Clear nail polish works well but smells and is also more than I'd like to spend, the brush worked well for application to the threads. The past several years I've been using a product called Fabri-Tac that is clear, waterproof, fast grab, and quick bonding, it's made by a company called Beacon in Mt. Vernon NY, www.beacon1.com. I thin it down with a reducer for automotive paint called Centari and use head cement applicator bottles to apply to the threads. You'll find many different methods of doing the same thing from the people on this site and all will work, this is just a method I've used that is fast, inexpensive, never comes undone.