How to implement a finger like joint

[RockyF]

This may be a constraint on the angle range, which constrains the rotation at a given angle, but the momentum of the upper limb will be passed to the lower limb, even if the upper limb is restricted by the angle.

[liabru]

Looks like you need an angle constraint, which is not yet implemented but please track this thread #71. In the meantime if you really need it, there are ways to do this using regular constraints or invisible body.parts that limit the motion.