I bought the three sizes from Tracy tools and did some measurements. These chucks use an adapter with a 1/2" screw in thread without a taper. I hacked off the tangs with my disc cutter and ground the ends flat. One adapter I drilled and tapped 10mm for my mill.

The measurement results on my mill are not great. The test bar was 8mm to cover all the sizes, 1/2", 10mm, and 5/16ths. The chuck body lengths excluding jaws are 57,50 and 50mm.
Measured the runout at the protruding end of the MT2 adapter at 0.2 thou (my mill runout). The chuck mounting face on the MT2 arbor showed a runout of 0.15 thou.
The runout next to the chuck body measured 7,4, and 1.2 thou respectively. At 1" this increased to 9.2,6.5 and 8.8 thou. The last measurement is pushing it a bit as at 8mm the test bar size is just over the 5/16ths the chuck is specified for.
Hope this helps anyone considering a purchase.
Best Regards
picclock
(Collet chucks rule)