These are (CF) Conflat CFF Bored Double-Sided, (same on both sides) CF 1-1/3 inches, Bored 0.63 inch, Through Holes, Stainless Steel, non-rotatable flanges. ConFlat (CF) flanges are used for ultra-high vacuum applications. These fittings use a copper gasket and knife-edge flanges to achieve the high vacuum seal and can operate down to 10-13 torr (10-11 Pa) and can be heated to 450 °C for bake-out. North American flange sizes are given by flange outer diameter in inches: 1-1/3 ("mini conflat"), 2?, 4?, 6, 8, 10, 12, 13?, 14 and 16?. In Europe and Asia, sizes are given by tube inner diameter in millimeters: DN16, DN40, DN63, DN100, DN160, DN200, DN250. These vacuum fittings are made of corrosive resistant stainless steel. 

Conflat Flange (CF) Bored Double-Sided, Bored 0.75 inch, Through Hole, 6 bolt, CF 1-1/3 inches, Stainless Steel

CF Flange Size: CF 1-1/3 inch, CF 1.33 inch

Common Dimensions: Flange Size OD = 1.33 inch 

A = 33.70mm (1 1/3 inch) 

B = 7.60mm (5/16 inch)

C = 16mm (0.63 inch)