There’s two types of commercially available ER20 collet nuts- one comes with M24x1.0 threads and the other comes with M25x1.5 threads.
When we were designing the MR-1 spindles we accidentally spec’ed an M24x1.5 thread on the drawing. By the time spindle shafts were in production, it was too late. The only option we had available was to customize the collet nut threads to be M24x1.5 to match.
We’ve got a good supply of these collet nuts now so we’ll make them available for purchase on the website.