Double threaded axel.....

Hmmmmm you mean for a track cog and lockring?

You do realise that it is the hub that has the threading, not the axel. the axel goes through the center of the hub, and the bearings on the axel which connect to the hub.

If you want a track hub, you have to buy one, is you have a Shimano freehub based wheel, then you can buy a Surly Fixxer, but it costs about $80. It is only really used when converting special wheels, like Carbon Wheels that are impossible to change the hub on.

Also, you can buy a new wheelset (front and back) for about $120, so not much point spending on a fixxer, unless you have a really expensive special wheel.

look at the top picture