SINCLAIR INTERNATIONAL produces stainless steel pilots for flash hole tools and Neck Thickness/Variance Gauges, designed to fit new, unfired case necks precisely.
The pilots are available for rifle and pistol cartridges ranging from 22 to 45 caliber, but are not suitable for use on .50 BMG due to its larger flash hole diameter.
This particular product is the 422 caliber pilot stop, specifically for the 404 Jeffery (.422-.423) caliber.