Old tool with a brass tapered cone and a folding knife blade — what is this used for?” the post asked. “The cone has measurement markings, and the knife folds out from the handle. Any vintage tool experts know its purpose?”
At first glance, it looks like something between a pocketknife and a machinist’s gauge — compact, elegant, and surprisingly precise. The brass cone’s markings suggest it was meant to measure something, while the folding blade hints at sharpening or cutting.
The truth is both simple and fascinating: this clever little device was used for sharpening hole cutters, specifically the kind made from brass tubing.
Before modern drill bits and precision punch sets, craftsmen often made their own tubular cutters to bore clean holes in leather, soft metals, rubber, or gaskets. Over time, the cutting edges would dull, and that’s where this tool came in. The tapered brass cone acted as a sizing and alignment guide for different diameters of tubing, while the small knife blade was used to carefully re-hone the edges — restoring a sharp, even bevel by hand.
It’s the sort of tool that combines practicality with ingenuity, built for craftsmen who valued maintenance as much as skill. Compact enough to fit in a pocket yet precise enough for fine work, it reflects an era when specialized tools were both functional and beautifully made.
So that mysterious brass cone with its folding blade isn’t a measuring tool or a miniature weapon — it’s a sharpener’s helper, keeping handmade cutters keen and ready for work long before machines took over the job.
