Can't be used to block is a trait given to some One-handed weapons, which disallows the ability to block with the weapon. All weapons with this trait are short, with a reach no greater than 60.
It is advised to have a shield when using a weapon with this effect due to the inability of the weapon to block by itself. However, while such weapons are incapable of normal blocking, they are still able to chamber block incoming melee attacks.
Weapons with this trait Edit
To be added...