Grade 18.8 / Phillips Drive / Round Head. Stainless steel round head machine screws have a semi-elliptical top surface and a flat contact surface. Machine screws are most often used with a nut as a means of tightening unless they have a pre-threaded hole with the exact thread pitch. These screws are most commonly offered in smaller sizes. Other types of machine screws sold at NutsandBolts.com are: phillips flat head machine screws
, phillips round head machine screws
and stainless steel flat head machine screws
. Phillips head machine screws are the most recommended type of drive. A phillips drive offers more control and less slippage.