Quote Originally Posted by Proteus View Post
explanation as to why the groove is missing in the top flange in their catalog
Because it's not a Coventry Easy Change tool holder.

I've just been and compared one to a BT30, and the Easy Change holders have a steeper taper, which would be correct as the Easy Change holder doesn't use a self locking taper, whereas the BT taper usually is self locking and needs force to remove it.
Unfortunately the battery is flat in my angle calipers and I don't have a spare, so can't give an exact angle.