Previous used Nikon CFI Eclipse Plan Apo 40x oil objective with sharp, clear, optics and a very high 1.0 numerical aperture.  Fully tested on a Nikon Ni-U with immersion oil with a glass slide with a 0.17mm coverslip by a Nikon factory trained microscope professional.  The objective tip is spring loaded and DOES NOT have any signs of wear or scratches or dents.  There is some fading on lettering from being touched during normal nosepiece rotation.  This is an infinity objective with M25 thread size, 0.16mm working distance, and works beautifully on the Nikon Eclipse models like the: Nikon NI-U, Nikon Ci-L, Nikon 50i, Nikon E400, and also the inverted infinity Nikon eclipse models like Ti2, TE2000, Ti-U, and similar Nikon microscopes. It is designed to be used with immersion oil, glass slides, and an ideal coverslip thickness of 0.17mm.  It provides excellent Brightfield, Fluorescence, Polarized, and DIC (Nomarski) images.  It will NOT work well on Nikon Optiphot and Labophot models that have fixed tube length optics and use the narrower, RMS thread, objectives.  It is 32mm in diameter, and 61mm long (measured from the objective collar to tip). The Nikon part # is MRD01400.  Free ground shipping only in the Continental USA via (seller choice) UPS, USPS, or Fedex Ground.