This property can only be read from. Attempting to write to it will cause an error.
This item is not replicated across Roblox’s server/client boundary.
The sum of the mass of all the
BasePart|parts in this part’s assembly. Parts that are
BasePart/Massless|Massless and are not the assembly’s root part will not contribute to the AssemblyMass.
Constraints and other physical interactions between unanchored assemblies with a large difference in mass may cause instabilities.