There are specials and then there are 0.8mm diameter metric screws  - turned from bar in steel, stainless steel or brass. Precision micro screws are a speciality of Challenge (Europe) Ltd who supply these tiny items mainly to the electronics and instrumentation industries.

They are used as critical mechanical components in micro assemblies, such as those found in clocks and watches, dials, computers, and a range of different types of medical equipment. These miniature parts normally require manual assembly processes under magnification.

Thread types offered covered BA or metric, and they can be supplied with compatible nuts and washers where required.