Hey Siegfried, You already have a Shief,. You must be ging to make binocular Shiefs. :^) Bill Kelley Does the loose nut have a name? Siegfried I have a bug up my butt to grind a 4.25" schiefspiegler. What do you think? I'd be starting with about 180 grit. I have a couple of old plate glass pieces. I wanted to see if Vaughn has some cervitt or zerodur or other low expansion glass.