Stoneskin Gauntlets - which knockdown does it affect?

Hi guys - can anyone who's tested it, or any experienced people tell me what kinds of knockdowns are increased in length by Stoneskin Gauntlets?

Is it only melee attack skills, or does it apply also to spells? (like some smiting skills, meteor, shock, signet of judgement etc.)

I'm pretty sure it's only melee skills. I have a pair myself.

Stonefist?
I use a pair of them, shock doesnt seem to benefit much, neither does backbreaker, but all the others do i think.

Ive tried it several times but it seemed they also work wid whirlwind.