Tennessee Code Title 67. Taxes and Licenses § 67-6-321

(a) There is exempt from sales tax the transfer, by any dealer in personal property, of railroad rolling stock or of vessels or barges of fifty (50) tons or over of displacement, where the purchaser gives the seller an affidavit that such rolling stock or vessels are being purchased for use in interstate commerce or outside this state; and any such rolling stock or vessels are also exempt from use tax, so long as they are being used principally in interstate commerce.

(b) There is exempt from the sales and use tax, the sale, use, storage or consumption of parts and accessories, material and supplies used in servicing and/or maintaining railroad rolling stock that is currently being used, or is reasonably intended to be used, in interstate commerce. Such exemption does not apply to fuel or other petroleum products or to shop equipment and tools.