Generally, sprinters use the least flexible shafts and marathon and surfski use the more flexible.
If more flex is the goal then pairing a blade with a softer shaft is recommended over a softer blade with a stiff shaft.
21K: Stiffness = 6.2. Designed in collaboration with Oscar Chalupsky for the Surfski market, or anyone looking for the softest, lightweight 100% carbon shaft on the market. 10cm of adjustment.
19K: Stiffness = 4.5. Designed in collaboration with Oscar Chalupsky for the Surfski market, or anyone looking for a more flexible, lightweight 100% carbon shaft. 10cm of adjustment.
17K: Stiffness = 3.3. Less popular, but often used for paddlers who feel the 19K may be too soft. 5cm of adjustment.
06K: Stiffness = 3.1. Popular for 735, 705 size blades on flat water, some mild ocean paddling. 5cm of adjustment. The most popular Sprint Kayak choice is 06K or 04K.
04K: Stiffness = 3.0. Popular 760 and 775 size blades for larger paddlers on flat water. 5cm of adjustment. The most popular Sprint Kayak choice is 06K or 04K.
03K: Stiffness = 2.8. Popular 775 and 815 size blades for largest sprint paddlers on flat water. 5cm of adjustment.
02K: Stiffness = 2.6. Popular 775 and 815 size blades for largest sprint paddlers on flat water. 5cm of adjustment.