If you look at old tool catalogues - 19th and early 20th century - you find that most 'kits' of brace bits included a range of centre bits, maybe one Jennings pattern twist bit referred to as a 'dowelling bit', several shell and nose bits for smaller holes, several countersinks, maybe a couple of screwdriver bits, and three 'reamers' or 'rimers'.
One of the reamers was square in section, tapered from about 1/2" to nothing, and about the same length as the one illustrated above. The second was half-round in section, and tapered from about 1/2" to nothing, exactly as the one illustrated above. The third was a bit longer, a bit larger in diameter at the fat end than the other two, and rather like a spoon shape in cross-section, with cutting edges on its long sided.
The reason for them was that old ironmongery and brassware was supplied with holes that may not necessarily fit the available screws (this being the time before standardisation of screw sizes) so the craftsman had to open out the holes in his metalwork to fit the screws he had to hand. The square reamer was for iron, the half-round was for brass. (The remaining scoop-shaped one was for opening up holes in wood.)
With the advent of standardised screw sizes in the early 20th century, the need for craftsmen to own reamers for their braces pretty much disappeared, as did the tools themselves. However, they still crop up quite a lot second hand, so there must have been thousands of them made and sold in the 19th century.
The illustrated one above is for brass, though the square for the brace chuck looks quite crude - though that may be the photo angle.