Just got my Sn3 axles from Mark Arscott at Markits. They fit the self-quartering drivers found in the UK. These are Scalelink 14mm, 3 foot in S scale.
Our HO Athearn/Roundhouse Mogul conversion to Sn3 with the new Scalelink drivers on the Markits axles. The Scalelink drivers have holes that tap for the Mantua style screws.
They work really well and make building Sn3 locomotives from HO mechanisms very easy.
Harold