It's been awhile, but IIRC, the one with durability is used as a weapon, and the other needs to be in your inventory when repairing a weapon yourself at an anvil. (Generally speaking though, you are much better off having a good weapon repaired at a Blacksmiths, and paying the fee; as doing it yourself will gradually keep degrading the weapon's overall durability over time, unless your skill is at 100%)

I can still repair items without the latter hammer (the unequibable one), and whether or not it is in my inventory has no effect on the resulting durability, (i,e, no increase in durability for having said hammer in my inventory, as one might expect.) A user on the Steam forums suggests it is likely to be a glitch. I'll look into it some more, a comment from an Arx Liberatis dev would be most appreciated.

Ahhh, okay. As I said, been a while since I played. That's what I remember the deal was with those two hammers back then. I'd be interested in what the real scoop is myself. If you do end up tracking it down, let us know...

I don't think there's any significance to it. It's just two hammers that are about the same but have slightly different stats for some reason. There are lots of decorative props in Arx. That's what the hammers are.

I just took a quick look into the game's scripts, and the usable hammer is a weapon, while the other is a "movable" (a useless item that you can only throw about). They share the same description, and weapon stats are hardcoded in language files, that's why they both have damage and strength requirements. There are no script events tied to the useless hammer, so don't worry about breaking your game.

Thanks. I'd imagine it should be made unpickupable in a future Arx Liberatis patch