One of the questions that gets asked a lot around here about installing drywall is what size drywall screws should I use. The Answer: What size screws to use will depend on the thickness and material of the studs you are attaching to.
For hanging 3/8 or 5/8 inch thick sheet on wood studs or joists, then 1 1/4-inch #6 coarse-thread drywall screws are a good choice.
For installing 3/8, 1/2 or 5/8 inch drywall on steel framing runners, channels or studs, then use 1 inch long #6 drywall screws. This applies to single layers of drywall. If you are installing drywall in laminated double-layer construction, additional length screws are required.
Drywall Screw Design
Drywall screws are made of case hardened steel. They are designed with metal piercing points and a bugle shaped Phillips heads which depressed the paper covering of the sheetrock underneath the head such that neither it nor the gypsum core are damaged. Defects caused by improper nail dimpling are also eliminated.
Drywall screws are usually black in color, which comes from a black phosphate finish on the steel. There are several types available, including coarse or fine screw threads, bugle head or trim head, and a high-low double threaded type for faster penetration and less stripped threads.
The drywall screw was invented in order to speed up drywall installations in commercial building with non-load bearing Interior wall partitions, most of which are supported with light gauge sheet metal stud framing.
Eventually they also began to be used with wood stud framing with success as well. New designs began to come out with courser threads to hold better in wood. These drywall screws have pull-out strength up to 3 1/2 times that of drywall nails, which allows for use of looser nailing patterns, saving time and money in wood frame construction. The broader range of applications also created a wider range of lengths.
So it is no wonder this is such a common question. It is really pretty simple, though. For most applications: 1 and a quarter inch length #6.