Here are some extant examples of Pinner's bones. These were one of the tools used by a pinner, or pin maker to aid in sharpening the end of the pin in a consistent manner.
The way the pinner's bone was used is demonstrated below. The pinner would obtain already drawn wire from a wire drawer. The image at the right is one of many depicted wire-drawers working at their craft. The pinner would take the hardened wire and lie it along the groove in the end of the bone with the future end of the pin pointing towards the bone.
In this position the pinner would use a metal file across the flattened portion of the bone. Using the file while slowly rotating the future pin would take off metal from the wire in a consistent manner so as to form a consistently shaped pinpoint on every pin.
In the image below the darker section of the wire would have been removed from the wire and the remaining wire would result in a consistently sharpened pin.
I'll be doing a demonstration at a future event on pin making. I've made a ton of pins, but have never actually used a period style pinner's bone. I usually use my small metal anvil. For the demo I created the pinner's bone depicted below.