商用方形窗戶，N-BK7光學玻璃*

I needed a square optical window with tight thickness tolerances for a small prototype, and these blanks are dead-on at +/- 0.125 mm. The surface quality is perfectly adequate for my visible-light testing.

The surface accuracy on these is impressive for the price — the 2λ per inch tolerance on the thicker windows made a real difference in my laser setup. They fit my mount perfectly with the +/- 0.125 mm diameter tolerance.

These square windows are noticeably cleaner than the cheaper ones I've used before, and the 2λ surface accuracy on the thicker pieces really shows in my interferometer setup. Each one came in within the ±0.125 mm thickness tolerance, so mounting them in my holder was hassle-free.