Eldi may be one of the venerable brands of back in the day but they are a bit crude no matter how you cut it.

Very long screw for a bicycle chain tool, any slack in it creates deflection and binding when extended.

This was probably a multi use tool for motorcycles too and everything in between, easily loosing its precision needed for small chains.

You might be able to find a grade 8 screw to use or you could have a pin made but my view would be to display it for its place in history.