GENERAL. Penetration gaging provides a means for determining the suitability of the Type 1A cross recesses formed in the heads of screws and may be used to indicate deficiencies in the dimensions of recesses specified in the dimensional tables for the respective screws. Penetrations which are too deep indicate the possibility of a thin section between the head and shank of screw, a weakness which might result in twisting-off screw heads during tightening of the screws. Use of screws having shallow penetrations might also results in production problems such as reaming of recesses or excessive wear on driver bits.