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There are actually two stacked toolkits somewhere in the game (in the zombie woman room, IIRC). But that's because stacking behaviour is inconsistently defined in multiple places. Another example is the fake lucky amulet that a goblin gang leader gives you — it can't be stacked. I don't agree toolkits should be stackable in their current implementation though, because each one has individual wear stats. However, they could be made a single inventory item (like lockpicks in Deus Ex), and each new toolkit pickup could add from 1 to 5 points to it.

There are actually two stacked toolkits somewhere in the game (in the
zombie woman room, IIRC). But that's because stacking behaviour is
inconsistently defined in multiple places.

Yeah, arx has separate maximum stack sizes for the player and NPCs.

I don't agree toolkits should be stackable in their current implementation
though, because each one has individual wear stats.

I'm not too sure either - and if implemented, it would be part of an optional mod, not the core game engine (it's scripted anyway).

However, individual wear is not a big problem as that's true for torches too and they are stackable - all items in the same stack simply must have the same wear value.

However, they could be made a single inventory item (like lockpicks in Deus Ex), and each new
toolkit pickup could add from 1 to 5 points to it.

So somewhat like the key ring, yeah, that could be possible. Again, that's something for a mod.

Hello, I have made a little mod based on your idea. You can download the result here. To install it, simply copy the 'graph' folder into your Arx Fatalis/Arx Libertatis installation directory. The mod only affects 1 file, lockpicks.asl from: graph\obj3d\interactive\items\provisions\lockpicks

It works like this: If you have two lockpicks, first with value x and second with value y, combining them (x with y or y with x, it doesn't matter), you will get a new lockpick with the total durability of x+y. You can combine lockpicks with different values (from 1 to 24), as long as the sum is not bigger than 25. Also, if you have two lockpicks, one with 20 and the other with 15, you will get two lockpicks, one with 25 durability and one with 10.

I hope this mod will satisfy your needs. If you feel like anything needs to be changed/improved, just contact me.

P.S.: Merry Christmas / Happy Hanukkah / Happy Kwanzaa or whatever you celebrate!