The binocular head I currently use on my Zeiss IM microscope is the Zeiss binocular head 47 30 11 9901. The dovetail is 43mm in external diameter.
I have included two photos of the IM microscope at the bottom of the page for colour comparison purposes – one taken using flash and one without. The binocular head is the same colour as the microscope. The Zeiss IM microscope is similar to the Zeiss IM35 microscope – in fact I have an IM35 as well and both are the same colour and use the same heads. Therefore, the colour of this microscope can be also seen on photos of the IM35 on the internet and many photos of the IM35 can be seen at this search link from Bing search engine: