The BQ-050-λ from Meadowlark Optics, Inc. is a Waveplate with Wavelength Range 400 to 1800 nm, Waveplate Thickness 0.005 Inch, 0.127 mm(127 µm), Waveplate Diameter(Inch) 0.5 Inch, Waveplate Diameter(mm) 12.7 mm. More details for BQ-050-λ can be seen below.