My B&L Stereozoom microscope didn't have any protection for the
objective lens assembly. It uses a rather oddball 38 mm threaded mount.
I thought that those with the same scope might be interested in the
adapter being sold as eBay 401250097157. It fits the 38mm thread on
the B&L perfoectly and adapts it to a standard 52mm filter thread.
Cheap--less that $3 shipped. Just got it today and it fits like a glove.
FWIW
--Chuck