These stiff metal brushes from RCBS are sized and designed to remove the spent primer residue from the primer pockets after the cases have been deprimed. A couple of twists of the brush and the case is ready for a new primer. Separate brushes for large rifle/ large pistol primer pockets and small rifle/small pistol pockets. Brushes have a standard 8-32 male thread, and fit the Sinclair Accessory Handle #09331S or many other brands of handles.
Big Book Catalog, Issue:67, Page:510
Sinclair, Issue:4B, Page:004
Sinclair, Issue:4B, Page:078