Thread Types:
Coarse Screw Threads:
Have more space between threads, making them suitable for softer materials like wood or drywall, and for sheet metal screws.
Fine Screw Threads:
Have smaller gaps between threads, ideal for pre-tapped holes in metal or use with nuts, providing a tighter hold.
Screw Thread Count/Pitch:
A higher thread count (threads per inch) indicates finer threads, while a smaller thread pitch (gap between threads) indicates a finer metric screw.
Shank and Thread Length:
Wood Screws:
Typically have shorter threads (up to an inch) and a smooth shank (threadless section) under the head, designed to prevent splitting or cracking wood.
Metal Screws:
Have longer threads (at least two inches) that cover the entire body below the head, and are designed for fastening metal and hard plastics.
Machine Screws:
Often have two types of threads: coarse and fine, and may not have a thread throughout the entire length of the screw shaft.