The Hamilton Converter is a simple frame that will fit and plug into the top of a conventional National brood box. The combined box and frame are then similar in internal size and shape to a 10 frame version of a B.S. Commercial (16" x 10") deep box, allowing the frames to run perpendicular to the original. This makes it easy for the beekeeper who has mixed National/Commercial equipment to use Commercial brood frames in a National box.
The Hamilton Converter is often advised for beekeepers who want to change from National to Commercial equipment, but the only advantage I see is it will give the beekeeper the opportunity of handling Commercial frames, without buying equipment, until they are comfortable handling the larger frames. To change once the decision is made can be easily done by placing the Commercial brood box above or below the National.
Construction is simple. There are four pieces of wood similar to an eke, two being machined to provide a protrusion that fits into the recess of the National box where the frames rest. These are easy to make with normal carpentry tools. It is better to make to fit existing hives, as there is some variation in dimensions between manufacturers, than for me to give dimensions. With a bit of ingenuity it could be made from bits, rather that machining. As they are only exposed to the elements during the summer and probably covered by the roof during the winter, they can be made from softwood.
Whether the converter is purchased from a supplier or home made I strongly suggest doing a dry run before fixing, as brood boxes are often slightly different sizes.
The late Bob Hamilton was a beekeeper from Horsham, West Sussex.