I should get out more. It is the Royal Microscopal Society thread devised in 1866 36 threads per inch of the 55° Whitworth form. The male thread has an outer diameter of 0.7965 inch (between 0.7952 inch and 0.7982 inch). The female thread, in the nosepiece, has a top-of-thread diameter between 0.8030 inch and 0.8000 inch. >From: "alanjstepney" <alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> >Reply-To: modeleng@xxxxxxxxxxxxx > >Whilst talking about unusual threads, there was a Whitworth for microscope >and telescope eyepieces, and similar optical equipment. It was probably >also >used on anything where a very fine thread on a large diameter tube was >required. >In that respect it is different from the Whitworth Instrument thread which >is of small diameter. > >Has any one any details of this large Whitworth thread? >alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > >www.alanstepney.info >Model Engineering, Steam Engine, and Railway technical pages. > > MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.