Screws have several technical terms associated with their various features and aspects. Here are some of the key terms:
Thread
- Thread Pitch: Measured in threads per inch (TPI) for imperial screws or the distance between threads in millimeters for metric screws.
- Thread Profile: The shape of the thread cross-section, such as:
- V-thread: Common profile for general-purpose screws.
- Square Thread: Used for high-load applications.
- Acme Thread: Similar to square threads but easier to machine, used in power screws.
- Buttress Thread: Designed for applications requiring high strength in one direction.
Shank
- Partially Threaded Shank: Common in wood screws, where the unthreaded portion provides a clamping force.
- Fully Threaded Shank: Common in machine screws, where the thread extends the full length of the screw for maximum holding power.
Head Types
- Flat Head: Sits flush with the surface.
- Pan Head: Rounded top with a flat bearing surface.
- Round Head: Fully rounded top.
- Oval Head: Rounded top with a tapered bearing surface.
- Truss Head: Wide, slightly rounded head.
- Bugle Head: Tapered underside for use in drywall.
Drive Types
- Phillips: Cross-shaped, self-centering.
- Slotted: Single slot, prone to cam-out.
- Torx: Star-shaped, high torque tolerance.
- Hex: Hexagonal recess, driven with an Allen wrench.
- Robertson: Square recess, common in woodworking.
- Pozidriv: Similar to Phillips but with additional contact points for reduced cam-out.
- Tri-wing, Torq-set, and Spanner: Specialty drives for tamper resistance.
Point Types
- Sharp Point: Standard for wood screws.
- Self-drilling Point: Has a drill bit-like tip for drilling its own pilot hole.
- Type 17 Point: A notched tip for fast starting in wood.
- Blunt Point: Used for machine screws and bolts.
Materials and Coatings
- Steel: Standard material, strong and versatile.
- Stainless Steel: Corrosion-resistant, used in outdoor or marine environments.
- Brass: Corrosion-resistant and non-magnetic, used in electrical applications.
- Aluminum: Lightweight and corrosion-resistant, used where weight is a concern.
- Titanium: High strength-to-weight ratio, used in aerospace and high-performance applications.
Coatings/Finishes:
- Zinc Plating: Corrosion-resistant, commonly used.
- Black Oxide: Provides mild corrosion resistance and a sleek appearance.
- Galvanized: Heavy-duty zinc coating for outdoor use.
- Phosphate Coating: Provides good paint adhesion and mild corrosion resistance.
- Chrome or Nickel Plating: Decorative and corrosion-resistant.
Length and Diameter
- Length: Measured from the tip to the underside of the head for countersunk screws or from the tip to the top of the head for non-countersunk screws.
- Diameter (Gauge): Varies depending on the screw type, measured in either a numeric gauge system (e.g., #6, #8, #10) or in fractional inches or millimeters.
Types of Screws
- Wood Screws: Designed for wood, with a tapered shank and coarse threads.
- Machine Screws: Uniform diameter along the shank, used with nuts or tapped holes.
- Sheet Metal Screws: Sharp threads for securing metal sheets.
- Lag Screws (Lag Bolts): Large wood screws with hex heads for heavy-duty applications.
- Self-tapping Screws: Can tap their own threads in materials like metal and plastic.
- Drywall Screws: Designed for attaching drywall to wood or metal studs.
- Deck Screws: Coated for outdoor use, typically have a bugle head.
- Set Screws: Headless screws used to secure an object within another object, like a shaft in a collar.
- Cap Screws: Used in precise applications, with a hex head and fully threaded shank.
Understanding these details helps in selecting the correct screw for specific applications, ensuring the right combination of strength, corrosion resistance, and ease of use.
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