These are .303" clearing plugs, also known as 'split case extractors'. They were found in the spare parts (or Section) wallet for the BREN gun, and were general issue for use with all British .303" weapons. Even those weapons such as the Vickers MMG, which were issued with special to type tools for this job, had these listed as an alternative issue. They were designed to be used when the base (or 'head') of the cartridge case separated from the body when extracted from the weapon breech after firing. This was usually caused by a combination of weak, poor quality, ammunition & excessive rates of fire combined with excessive headspace. When it happened the only way to remove the portion of the case stuck in the chamber was to use this tool. It was pushed into the chamber by hand and the breech closed over it. This forced the spring steel prongs through the front of the case. When the breech was opened the prongs were forced out by the stem, gripping the neck of the case and pulling it free of the chamber. The tool could then be dismantled by unscrewing the base and the case removed. Clever. Original issue in good used condition.Stock No 17/6.