Precision Cylinder Mirror, R17.5 x 27.6 Polished to meet Acton standards detailed in "surface ... .doc" file Precision Cylinder Mirror, R17.5 x 27.6-BK7-27.6mm x 8mm x 2.4mm (center)-Trapazoidal cuts as described ... : Striation free under 100X microscope Precision Cylinder Mirror, R17.5 x 27.6