Not all screws are the same. While they all have external threading, some of them are designed differently than others. Fortunately, you can often refer to abbreviations to identify screw types.
FH
Screws with the FH abbreviation are flat-head screws. Also known as countersunk screws, they feature a flat head that’s tapered on the side. Flat-head screws will rest flush with the surface of the material in which they are installed.
BH
You may come across screws with the BH abbreviation. The BH abbreviation indicates button head. Button-head screws have a dome-shaped head, which allows them to protrude out of the material in which they are installed.
MS
One of the most common screw abbreviations is MS. MS screws are machine screws. Machine screws are short, heavy-duty screws that feature uniform threading. As their name suggests, they are used in machine-related fastening applications. If you need to hold two or more machinery parts together, you should consider using a machine screw.
PH
Screws with the PH abbreviation feature a Phillips head drive recess. The top of the head, for instance, has a cross-shaped cutout. To install a Phillips head screw, you’ll need to place a bit of the same type in this recess, after which you can turn the bit clockwise. Screws with the PH abbreviation are characterized by a Phillips head drive recess such as this.
FT
Some screws have the FT abbreviation. The FT abbreviation indicates a fully threaded shank. All screws have a shank. The shank is the main part of a screw. Screws have a head, followed by a shank. If you come across a screw with the FT abbreviation, it’s safe to assume the shank is fully threaded. Threading will completely cover the screw’s shank — all the way from the head to the tip.
SH
While not as common as a Phillips head, some screws have a socket head. Socket head screws typically have the SH abbreviation. They still have a drive recess. Socket head screws, however, don’t have the same cross-shaped drive recess as their Phillips head counterparts. Rather, they have a hexagonal recess. You can install them using a hex key or socket bit.
STS
The STS abbreviation indicates that screw is self-tapping. They feature a tip that’s similar to the tip of a drill bit. With this tip, self-tapping screws are able to tap their own.
SS
The SS abbreviation may have different meanings. In some cases, it’s used to describe screws made of stainless steel. In other cases, the SS abbreviation is used to describe set screws.