The MBXXXX2XX from S&R Optic GmbH is a Waveplate with Wavelength Range 400 to 1550 nm, Waveplate Thickness 2.5 mm, Waveplate Diameter(Inch) Outside 0.2 to 0.78 Inch, Waveplate Diameter(mm) Outside 5 - 20 mm. More details for MBXXXX2XX can be seen below.