GetMass returns the value of the read-only
This function predates the Mass property. It remains supported for backward-compatibility; you should use the Mass property directly.
The part’s mass
Finding a Part's Mass
This example creates a new part, myPart, in the game’s Workspace, with dimensions 4x6x4 studs. The part is also anchored.
Then, myMass is set to equal the mass of the new part. The mass of the part is printed at the end of the print statement:
My part’s mass is …