Anatomy of a Screw
A screw is simply a cylinder surrounded by ridges called threads. The top, the part that is visible after the screw is installed, is the head. Directly below the head lies the shank, a smooth area of the screw with no threading; not all screws have one. The rest of the cylinder is called the shaft. Screw height is measured from the end point of the screw shaft to the head.
Screws come in a number of different materials, including stainless steel, brass and aluminum, and can be covered with coatings such as zinc or black oxide that promote durability and ease of use with various materials.
Types Of Screw Heads
The screw head is where the force is applied. The various types of screw heads are designed to accept different driving instruments to distribute the force effectively.
The standard slotted head is best used with a flat screwdriver, while the cross-shaped indention is best suited to a Phillips screwdriver. A Robertson screw has a square-shaped indention and requires a matching driver head.
There are two types of hex screws: An Allen screw has a hexagonal indent in the head, requiring an Allen wrench, and the other type has no indent in the hexagonal head and must be applied or removed with a socket wrench.
While screw heads have evolved to include expanded and combined head designs, most drill bit sets come with multiple bits and bit guides to show you the head design that will suit the bit. Match the drill bit to the screw head size and design and you’ll have a much easier time attaching the fastener without stripping the head.
Common DIY Screw Types
There are five different types of screws that the average DIY enthusiast will work with on a regular basis.
- Coarse threads, smooth shank, tapered head
- Available in interior and exterior styles
- Use for basic wood construction
- Choose a length that will penetrate the lowest board by 2/3 of its thickness
- Need a pilot hole drilled unless screw is self-tapping
- Similar to wood screws
- Resists corrosion
- Head is designed to countersink
- Use to attach decking to the deck frame
- Composite decking needs decking-rated screws
- Head designed to countersink without damage to drywall
- Requires drywall dimple bit – not usually included in a standard drill set
- Use for drywall installation only
- Standard screws for wood studs; metal studs need metal-rated screws
- Tip is flat
- Most are hex-head design, some have Phillips head
- Also called an anchor
- Must pre-drill holes prior to installation – requires hammer drill and masonry bit
- Anchor can be installed with a standard drill
- Star-drive heads
- Require matching driver bits
- Designed to pierce without splitting material
- Use with MDF material
- Avoids having to drill pilot holes
Other Types of Screws
Torx/TORX Plus Screws:
- 6-point star indention
- Requires TORX driver bits
- Design prevents screwdriver from slipping
- Often used on electronics
- Two parts – male and female end
- Slightly domed head
- Primarily used in bookbinding and leatherworking
- Variations on standard screws
- Special bits required to install and remove
- Mainly used in public works to prevent vandalism and theft
- Sharp points, flat or hex washer heads
- Available in a range of sizes
- Primarily used for metal – can be used to secure multiple materials together
- Much stronger than standard screws
- Coated to resist rust
- Finer threads made more precisely
- Used for joining machine parts
- Hex head
- Must drill a pilot hole to install
- Requires a ratchet
- Used for joining metal to wood
From wood screws and deck screws to the specialty screws of machining or metalwork, the right fastener will make a huge difference in your projects. Learn to match the screw to the material and make sure your project is the best it can be.
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