Designed to fit into an eyepiece on an M3600, M3700, M3, or M3-F series microscope, the Swift Optical 19mm Eyepiece Reticle with Retaining Ring can be used to measure or count small or microscopic specimens and particles. A simple crosshair reticle allows you to easily center the specimen in the field of view or group particles into different areas with clear delineation between groups, and a 10mm long scale on one axis with 100 divisions enables you to more easily measure a sample. The reticle is held in place in the eyepiece with the included retaining ring.