Tenn. Code Ann. § 55-1-117

“Fixed load vehicle” means any vehicle not designed or used to carry, convey or move any freight, property, article or thing over the highways, except its own weight of any equipment, appliance or apparatus constructed as a part of, or permanently attached to, the body of the vehicle. “Fixed load vehicle” includes well-drilling apparatus, cranes and portable feed mills and such other vehicles as are within the general terms hereof, the primary use of which is not upon the highways and streets of this state, but does not include wreckers or tow cars equipped with cranes, hoists or dollies and used for transporting wrecked motor vehicles or motor vehicles designed to deliver ready mixed concrete.