A combined sun & star diagonal, designed by Alexander Clarkson, made by W. Watson & Sons of London, circa 1900.
R.A.S. standard 1 1/4 inch thread.
With other parts.
Marked: “SUN” & “STAR” DIAGONAL. – W.WATSON & SONS, LONDON.
For more information on combined sun and star diagonal see the paper written by Chris Lord: http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/PageMill_