Quoted from markmon:
PDI glass is 3/16" thick just like all other glass. I had my wiz glass way too tight to remove also. I filed out the inside of the plastic channels until it was manageable.
If the glass is coming from Europe, it's generally either 4mm (.15748 inch) or 5mm (.19685) whereas 3/16 = .1875 ... anyone can take some calipers as I don't have either here, but my guess is the 5mm if it's a tight fit.