Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 159

The standard height of draw bars for freight cars, measured perpendicularly from the level of the top of the rails to the centres of the draw bars, shall be thirty-four and one half inches for standard gauge railroads and twenty-six inches for narrow gauge railroads, with a maximum variation from such standard height, in either case, of three inches between the draw bars of empty and loaded cars; and no freight car with draw bars which do not comply with the above standard, whether loaded or unloaded, shall be used in moving traffic between points in the commonwealth.