My advice on adjustable pen mandrels: Don't buy one!
As a followup to my earlier post regarding 0.012" runout on, not one, but two of these:
(Recall that this mandrel consists of the rod itself in a 1/4" collet on a #2 MT.)
Before returning the second one to Craft Supplies, I took it to Woodcraft to test it in their Jet mini. Same problem (i.e. the morse taper fit was poor, and noticeable runout at the collet). Then, I tried a Woodcraft adjustable mandrel (same design, different finish), and though the morse taper fit was a little better, the runout was visible by eye.
So now it seems to me that the poor quality is in the collet itself, which is not too surprising when you look at it. You can't expect those 4 short tangs to compress equally. And, when you compare it to, say, Beall's 1/4" collet (at $80) you can see where the improvement is!
Lee Valley sells an adjustable mandrel which, rather than a collet, clamps the rod with a set screw in the MT. This has possibilities so long as the hole for the rod is drilled slightly off-axis to allow for the set screw pushing it to one side. If not, whatever tolerance there is in the hole diameter will equate directly to runout.
For now, I use a replacement mandrel (rod only) in my Jacobs chuck. No measureable runout.
Regards, Tom