1/4 x 1-3/8 UNC Machine Screw Phil Fillister in A2 Stainless - ASME BA18.6.3
UNC Phillips Fillister machine screws have a large cylindrical head, with a slightly convex top surface.
Fillister head screws are the preferred head type for counterbored holes and can also be used for protecting
a surface by raising the level by which the tool is used to tighten the fixing. They are similar
to a Pan head machine screw, but with a greater head height. Height to diameter ratio is also larger than a
cheese head. Imperial Unified Coarse thread version.