26 mm is best for paddles with a 15-16 mm core (These usually have an edge guard that makes the paddle width 18-20 mm total). This also fits well on paddles like the Selkirk Luxx 20 mm paddle.
23 mm is best for paddles with a 12-14 mm core.
If you are unsure which size is best for you, 26 mm is usually the safe option. However, please message us if you have questions!
