Sword mastères for act5 merc

Maybe a stupid question but I didn't found the answer yet.
If I found a barb

Helm base for Cure, Delirium for example and give it to my act5 merc. Does the bonus of Sword masteries will benefit to the merc (if the base roll with SM of course ?
(Sorry for my english I'm from France, did my best )

i think the following is correct:
+ to a single skill (that the merc has) works
eg +5

Frenzy from Fury, barb

Helm with +2

Iron Skin
+to skill tabs do not work, eg +2 combat skills from

Arreat's Face
+ to barb skills work, eg +2 barb skills from

Arreat's Face
+ to all skills work, eg chain of Honor

Yea the merc will only receive +skill points to skills he already has. So unfortunately if you give him the sword mastery

Helm, it won’t give him the skill, just like if you give him a +

Battle Orders

Helm, he won’t cast it

Indeed, like previously mentioned, the

Harrogath Barbarian will only benefit from +skills that he already has. He basically has 3 skill trees, with a single skill in each.

This does include "+all skills", "+barb skills" and "+tab skills". +Tab skills work exactly like they would on a player character, e.g. +2 Masteries will increase the dual wielding barbarians

Iron Skin level by 2.

Additionally oskills work, albeit only passive ones like

Critical Strike and

Dodge. If there was an item with +sword mastery as an oskill, the barbarians would be able to benefit from it.