Thermold followers are non-standard and unaltered USGI followers will not fit.

-Troy

I did a couple for both Thermolds and Orlites (both required modification, and different mods for each type).  If you compare a Thermold follower with a GF, you will see that the Thermold has slightly different cut-out areas and grooves in the mag body, so you have to remove some material from a USGI follower in order for them to fit.

Note that 30-round Thermolds already have an anti-tilt leg (it's small and short, but does okay).  I don't remember if the 20s do or not.

Anyway, I DO remember that I had to use sanding discs on the Dremel at fairly low speed to remove the material from the follower, or else the plastic would just burn and melt.  It was a pain, and IMO not worth doing for plastic mags in the first place.  I was doing it as an experiment rather than to gain real value from the mags in question, but for most purposes, you're better off buying USGI mags to start with.

-Troy