This listing is for a vintage Spencer Lens Co. microscope mechanical over-stage.  It's a versatile type with above-stage x/y thumb-wheels and when fitted to a suitable microscope transforms both the look and the ease of use in terms of specimen positioning.  The item attaches to the right hand side of the stage with a couple of thumb-screws that are tightened from below and you'll see in the listing photos that I attached the over-stage to a Watson Service model for demonstration purposes.  It's very easy to fit and remove.

As well as the Service, I've also used this model of over-stage successfully with Edinburgh-F, Fram and other Watson models with plain stages in brass or ebonite.  The Spencer over-stage can fit plain stages up to about 12mm in thickness, so is suitable for many types of plain stage from a variety of manufacturers.  I've included some photos at the end of the listing of a similar (slightly later) Spencer over-stage fitted to a Watson Fram dating to about 1908 and you'll see that it fits that type of stage really well.

The over-stage is fully working with x/y axes moving smoothly and just enough resistance so that the y-axis doesn't slip on inclination.  The sprung arm works well and both slide holding arms can be positioned and tightened into place with brass thumb-screws.  All-in-all a very good vintage accessory.

The over-stage will be very well wrapped and shipped by Royal Mail.

Thanks for looking.