It is an adjustable reamer which is slightly different from the common type as it has helically cut blades. This is to reduce the chatter common with straight bladed reamers. The maximum and minimum sizes it can span should be stamped on the shaft.

If I remember correctly, as a hand reamer, they also have a generous lead-in.

Adjustable reamers of this type are sometimes sold as sets with both 'straight' and 'helically cut' blades. For some reason, adjustable reamers command silly prices second-hand (even if looking well beaten-up) here in NZ. Unpleasant to use, in my limited experience. If anyone can offer advice about how to sharpen the blades (properly), I'd be grateful…

I bought a beautiful Hilger & Watts (IIRC) micrometer water level in UK in the late 90's (?) for very little money. It was considered merely a curio then, so I suppose laser levels had already taken over. Or, perhaps, prevision levels, autocollimators, etc. One day, perhaps I'll use mine, but for what?