540 Mass. Reg. 22.10
Except for motor vehicles and trailers which must comply with the federal requirements referenced in 540 CMR 14.00, when any vehicle is used to tow a trailer on the ways of the Commonwealth, two safety chains shall connect the trailer and the towing vehicle, one on each side of the central trailer hitch. One end of each chain shall be securely attached to the towing vehicle and the other end securely attached to the trailer in such a manner as to control the direction of travel of the trailer and prevent the tow bar dropping to the ground in the event the coupling fails. Each chain with its means of attachment shall be entirely independent of the other chain or of the coupling and shall have an ultimate strength at least equal to the gross weight of the trailer and its load. The chains shall not be permitted to drag on the ground and shall have no more slack than is necessary to allow proper turning of the vehicles.
540 CMR 22.10