Mo. Rev. Stat. § 389.830
From and after the first day of January, 1908, it shall be unlawful for any person, persons, company or corporation, operating any line of railroad, in whole or in part, within this state, whether as owner, lessee or receiver, to use any locomotive, tender, car or similar vehicle for the purpose of carrying persons or freight, on its line of railroad, between stations wholly within the state, unless such locomotive, tender, car or other similar vehicle shall be equipped with standard drawbars; that the standard height of drawbars on all standard gauge roads shall be thirty-four and one-half inches, measuring from the top of the track rails to the center of the drawbar; and upon narrow gauge roads such standard drawbar shall be twenty-six inches from the top of the track rails to the center of the drawbar, and the maximum variation from such standard height to be allowed between empty and loaded cars shall be three inches, whether or not the drawbars brought together are of the same kind, make or type.
§ 389.830, RSMo
RSMo 1939 § 5237