If you have a Thomson Elite, Masterpiece or Dropper seatpost with the standard clamp, you can only use 7x7mm saddle rails (alloy, steel or carbon). If you want to run a saddle with 7x10mm oval carbon rails, such as a Fizik option, you need replace the stock modular clamp with this Thomson Seatpost Clamp for Oversize Rails.

You get the same long 1.614 inch (41 mm) seat rail grip length and Infinite Tilt Adjustment from minus 5° and plus 29° angle. Of course this oversized rail version also has the same high strength 7000 series aluminum construction. You don't need longer bolts, the originals are long enough, but if you want or need to replace your bolt assemblies, those are sold separately, but available.