I saw this on eBay and I remember my uncle telling me a rumor that before the 14 karat gold masks were made they tested the casts with silver or pewter. To make sure the masks would fit on the head without scratching the official headpiece.
Note: whoever this guy is on eBay. I’m pretty sure they owe one of the metal casts. Even though Lego said that they “destroy their casts” I’ve Heard of people not only finding them but restoring them to full function so they can create their own things. I think this guy is one of them mask does work on official heads. Also mask is not magnetic.
Here it is Right next to a regular skull Spider mask. You’ll see not only that there are no official stamps for the circular bits on the regular one are not on the metal one that clip the mask into the head.
And yes official Lego pieces on the side clips do work on it with no stress and nothing hindering anything. I can’t wait to use this for my next moc. Hope you all enjoy