There really isnt a lot that can be said about a metal spring except that this simple innovative tool from Marc Petitjean can make the tying of flies a lot easier. When using the split thread method for dubbing the use of this spring allows the tier to tie in two different materials. A poor explanation may be that the tier splits the thread uses a pair of scissors to keep the loop open, adds the material using the Marc Petitjean Magic Tool clip (or similar) then before removing the scissors fits the clip to secure the first amount of material. The second amount can then be placed in the split thread loop using the same method. 
All a bit difficult to understand then have a look at this video on YouTube which hopefully will help you 
https://www.youtube.com/watch?v=n5fPOlrYhbY

As always these items are sent out with a post inclusive price using a first class service provided by Royal Mail. Items will be sent on the same working day as your purchase if ordered and paid for before 3pm. It may be the case that you wish multiple items and we offer a discount if you get in touch via phone or email.