Like resin temperature, viscosity and messing about with vacuum chambers! An increase in hoop strength by 28%! These are probably the strongest blanks in the world.Even though we were working with a higher modulus carbon than the XL50 range the actions are almost identical so even though we wanted a powerful super fast action these blanks are light, responsive and parabolic (so not poker stiff). For experienced rod builders you will notice I have posted a picture of the butt "walls" to show uniformly they have been rolled. The picture with the blank under stress is me pushing the blank vertically towards the ceiling with maximum force, hence the very weird "T" shape!!! DONT TRY THIS AT HOME! Finished in a deep royal blue with the following specifications. Butt OD: 10.74mm/0.378. Tip OD: 1.77mm/0.069. I can also supply the blank with a full kit of components, the price will depend on what you need so please feel free to. Building a fly rod is not difficult but there are a few tips and tricks I will be happy to share with you if this is your first build. Add a map to your own listings. For more information on building your own fly rod check out my Bloke fly rods Youtube channel. This item is in the category "Sporting Goods\Fishing\Rods & Poles". The seller is "mickgbe" and is located in this country: GB. This item can be shipped to North, South, or Latin America, all countries in Europe, all countries in continental Asia, Australia.