Hey there @unrealengine432! So it looks like due to the objects being welded, you cannot get their mass independent of each other.
You can get the individual mass by not welding the objects. However, to utilize it’s parent’s simulated physics and rigid body it would need to be welded otherwise it would throw a (non-fatal) error when something touches it. Depending on your use case, you could save the parts individual masses to a variable and then reference that even while they are welded.