The BP208 from Thorlabs Inc is a Beam Splitter with Beamsplitter Diameter I.D-50.8 mm(2 Inch), O.D-60.3 mm(2.38 Inch), Beamsplitter Thickness Frame Thickness 4.8 mm(3/16 Inch), Operating Temperature -40 to 70 Degree C, Wavelength Range 400 to 2400 nm. More details for BP208 can be seen below.