SINCLAIR INTERNATIONAL manufactures precision machined stainless steel pilots for flash hole tools and Neck Thickness/Variance Gauges.
The pilots are designed to fit new, unfired case necks for rifle and pistol cartridges, specifically available for 22 thru 45 caliber, excluding .50 BMG.
This particular product is a 41 Caliber Pilot Stop, suitable for .410-.412 caliber cartridges.