Originally Posted by DWalt

The grip style shown is from 1969 or later, as there is no diamond around the screw holes. It is often called the "PC" (plain clothes) style due to the rounded corners at the bottom. That style was used on M&P service revolvers (but not K-frame target revolvers) from the early 1950s onward. The idea was that the rounded bottom corners, when carried concealed, did not visibly print through clothing as much and also reduced wear on clothing such as jacket linings.