IWD2 uses modified rules for weapon specialization, mastery, high mastery, and grand mastery (or **, ***, ****, and *****, respectively).

Weapon Specialization (**): Available to fighters at 1st level. Available to rangers, paladins, and barbarians at 3rd level. Character gains +1 attack bonus, +2 damage while using that weapon type.

Weapon Mastery (***): Available to fighters at 3rd level. Character gains +3 attack bonus (total), +3 to damage (total) while using that weapon type.

Weapon High Mastery (****): Available to fighters at 6th level. Character gains +3 attack bonus (total), +3 to damage (total), and an addition 5% chance to critically hit while using that weapon type.

Weapon Grand Mastery (*****): Available to fighters at 9th level. Character gains +3 attack bonus (total), +3 to damage (total), an addition 5% chance to critically hit (total), and a 10% chance to stun (Fort save vs. 20 DC, lasts one round) while using that weapon type.

NONE OF THESE SPECIALIZATION LEVELS GRANT ADDITIONAL ATTACKS.

If you are dual-wielding, you gain an additional attack with your off-hand at your highest BAB. Of course, modifiers can lower this amount, especially if you don't have any points in TWF. You never gain more than one attack per round with your off-hand.