City 4 rear axle size ?????

[Rboate]

I wanted to install a trailer adapter on my City 4 but the thread on the axle barely protrudes past the axle nut, if I added the hitch mount I'm not sure the nut would tighten sufficiently.  I have seen both Burley and Thule make an adapter that replaces the nut and has a threaded shaft to connect the hitch to.  My question is does anyone know for sure what size the axle is and the thread pitch.  By my measurements it looks like 12mm 1.00 or 1.25