Thorlabs' cemented near IR achromatic doublets are available pre-mounted in engraved threaded mounts, making it easy to incorporate these optics into your setup.
The engraving on mounts 1/2" or larger in diameter clearly indicates the part number, focal length, and antireflection coating deposited onto the surface. The engraved arrow indicates the direction of light propagation to collimate a point source, and an infinity symbol denotes that this lens has an infinite conjugate ratio (i.e., if a diverging light source is placed one focal length away from the flat side of the lens, the light rays emerging from the curved side will be collimated). Mounts smaller than Ø1/2" are engraved with the part number only.