Axle Question

[jawsrider]

I am looking to buy a bicycle trailer to haul my child behind my Radmini.  I believe I need to buy a hitch adapter, so that the trailer can connect to the rear axle.  Does anyone know what the diameter and the thread pitch are on the rear axle?

The adapter diameter and thread pitch options that I can buy are the following:

1) 3/8 x 26,

2) M10 x 1.0

3) M10.5 x 1.0

I am not sure which is compatible with the Radmini.