I believe these two different embossed PHILCO and CORWICO nail knobs were made by Cook Pottery Co. The molds for these are similar to the Cook one that doesn't have the ribs inside. The one PHILCO is the grey porcelain with black glaze and the other PHILCO is white porcelain with black glaze. The CORWICO and CORWICO U.S.A. pieces have a same inside base as the Cook without the ribs.