From Fantastic Wiki

Joints are the linkages between parts. Joints are the only thing in the game that experiences any sort of stress. With enough force, a joint can break and the linkage between the linked objects will no longer exist.

[edit] Properties

[edit] Elasticity

Because joints experience stress, they have some elasticity. When used in a chain, they can be used as spring or to phase through other objects. Putting the chain under too much stress can cause the joints to break. Normally this is inconvientient, and results in the player having to increase the individual chain lengths, as the game's physics presents that the joints are stronger for longer sticks. However this can be used for water break catapults.