The BP533 from Thorlabs Inc is a Beam Splitter with Beamsplitter Diameter I.D-12.7 mm(1/2 Inch), O.D-19.1 mm(0.75 Inch), Beamsplitter Thickness Frame Thickness 4.8 mm(3/16 Inch), Operating Temperature -40 to 70 Degree C, Wavelength Range 635 nm. More details for BP533 can be seen below.