But it is possible with an adapter. I run my 24" Qu-Ax steel frame with disc brake having no issues.
See here: Euer setup
A simpler setup is here: Euer setup
The d’Brake doesn’t care about using a nut or a thread in the frame. The only important thing is to hava a planar surface to transfer the force from the brake into the frame. More info here: Nimbus D-brake -vs- Mountain Uni UCM brake mounts
