… in late Colonial and Regency corsets, was much like today’s paint stirrer but much thicker and more durable. Typically made of a hardwood such as oak and maple, it was about 1/8″ thick and 1 1/2-2″ wide early in the Regency era, widening to 2 1/2″ later. Early it was tapered, while later it was straight.
The purpose of the busk was to distinctly separate the breasts to put them into the cups provided by the corset so they were clearly “two pert apples on a tray” to quote a cartoonist at the time.
(Extant corset 1830’s with a modern sketch for replicating the cording of the historical example)