These are the original Dave Clark axle shafts manufactured in the USA. A long time standby of racers and long distance tourers alike, these axles are a huge improvement in strength and design over original axles and modern stock replacement axles. The threaded end is drilled has a second hole for the cotter pin making alignment for proper torque easier. These axles are threaded for the UNF thread used on TDs from car 12285 and all TFs. These axles will fit TDs before car 12285, but you will need to use the 14 TPI castle nut (27-029 or heavy duty 27-029C).
http://www.ttalk.info/HalfShaftReplacement.htm