Update: I only just now realized, when adding the new parts discussed below, that I completely forgot to add the collision and connectivity files for all of the parts. They have now been added.
Chain Update:
I’ve always found the chain parts in stud.io difficult to work with. Since the only connection points are at the ends, it can be difficult, or even straight-up impossible, to get a chain to follow tight corners, or wrap around something. So, I separated a chain into its separate components, which can be assembled in stud.io and individually posed:
Each link has a ball connection on one end, and a socket on the other; as such, there are two end-links: one with a socket, and one with a ball. All three parts are needed to make a full chain in stud.io.
The primary goal behind doing this was simply to allow for tighter, more precise posing of official chain parts, such as on the sword that inspired me to do this in the first place:
However, the parts can also be used for various non-purist purposes in stud.io, such as creating custom lengths of chain:
Or open-ended chains:
Note that, if you generate a parts list in stud.io with these parts, each link and/or chain end will be counted an an individual part, and they will all be lumped together with any official 16-17L chain parts used in the model, due to the fact that all three of these custom parts use the same part number.
For example, if you make a model with one copy of the official stud.io version of Part 30104 and one copy made with these custom parts, stud.io will tell you you are using 24 of the part; 21 custom links, two custom ends, and one official version of the full part.
EDIT: I also just added a fixed version of Part 10049:

The connection in the official version is wrong, so it can’t actually be held in a clip.