US Patent 10036412 Counterbore plug

A counterbore plug comprises a generally cylindrical annular body defining: a cylindrical axis and a radial direction, a first end and a second end that are disposed along the cylindrical axis, an aperture that extends at least partially from the first end to the second end, the body including a radially inner annular surface, a radially outer annular surface, and a plurality of projections that extend radially from the radially inner annular surface that at least partially define a polygonal perimeter.