Default DX-6 or matching Melee-2
A flail is any flexible, unbalanced weapon with its mass concentrated in the head. Such a weapon cannot parry if you have already attacked with it on your turn. Because flails tend to wrap around the target’s shield or weapon, attempts to block them are at -2 and attempts to parry them are at -4. Fencing weapons and knives cannot parry them at all! An unarmed fighter can parry a flail, but at -4 in addition to any penalty for parrying unarmed.
See also: Buying Weapons and Armor