Up for sale is a New, Dual-Side 24mm Diameter Reference Flat accurate to 1 micro-inch (1/20 wave band).  Side 1 is reference grade, Side 2 is working grade.  New from old stock, still in original packing material.  The flatness of this part is verified as shown in the monochromatic flatness images of both sides to 100% of this optical flat being compared to a larger reference grade flat in the photos.  Made from fused silica, this optical window has the hardness, & low expansion coefficient for your project needing a precision reference flat or window.  You can't make what you can't measure so this will give you the ability to guarantee flatness.   Both sides are un-coated.  

SPECS:

Substrate: Fused Silica

Diameter: 1" (24.0mm)

Thickness: 1/4" (5.45 mm, +/- 100 um)

Serial Number: ^

Accuracy Side 1: REFERENCE GRADE 1/20 wave band 546nm

       0.000,001 inch (1 micro-inch)

Accuracy Side 2: WORKING GRADE 1/8 wave band 546nm

       0.000,003 inch (2.7micro-inch)

Evaluated conformance 9/28/2025

As always, your complete satisfaction is guaranteed.  If not 100% satisfied with this, you may return.  I have many happy customers and would like you to become one as well.  Sizes up to 5” dia. available.  

Winning bid to pay $5.40 shipping within USA.