Spectacle Blinds

Dimensions Spectacle Blinds – ASME B16.48

General Notes:

Dimensions are in millimeters unless otherwise indicated.
D = Hole size (where required) should be the same as the flange bolt hole. In practice, these dimensions have been rounded round off upwards.
Wt = Thickness of the web (or tie bar) should be 6 mm minimum, or equal to Thickness (t) if less than 6 mm. Spectacle Blinds should be made from a plate or forging specification, approved for use by ASME B31.3, of essentially the same chemical composition as the mating flanges and piping involved
Spectacle Blinds according to ASME B16.48 may be used for installation between ASME B16.5 flanges
Depending on a customer specification, some dimensions can be different from what on this page is defined.

ASME B16.48 says: The gasket seating surface finish and dimensions for raised face line blanks shall be in accordance with ASME B16.5. A raised face may be specified at the option of the purchaser.
A Raised Face would add machining time and complexity so the price would be higher. Call this the Bugatti or Rolls Royce of the line blind world.
Personally, I have seen that version once or twice somewhere. The version without Raised Face is the default and is used everywhere.