What are Fishtail Screws? Characteristics and Structure
1. Self-Drilling Lag Screws: Definition
Self-drilling lag screws, also known as self-tapping lag screws, are a type of fastener that features a quadrilateral (four-sided) umbrella head and a fishtail drill tip. These characteristics enable the screw to penetrate hard surfaces like steel, wood, and drywall without the need for pre-drilling or pilot holes, saving time and effort during construction and equipment assembly.
Construction:
Umbrella Head: The head resembles an umbrella, increasing the contact area when driven, providing greater clamping force, and ensuring a more secure connection.
Fishtail Tip: The tip features longitudinal grooves that facilitate self-feeding into the material as the screw is turned.
Threaded Shank: The shank's deep threads engage with the material, creating a strong bond between the screw and the substrate.
Drive Head: The head allows for driving the screw using a screwdriver or power drill.
Materials:
Carbon Steel: Most common, offering high strength and affordability.
Stainless Steel: Excellent corrosion resistance, suitable for harsh environments.
Plastic: Lightweight and electrically insulating but lower load-bearing capacity than steel or stainless steel.
Brass: Conductive and corrosion-resistant.
Dimensions:
Diameter: M6, M8, M10, M12, etc.
Thread Pitch: 1.0, 1.25, 1.5, etc.
Advantages:
Time and Effort Saving: No pre-drilling required, streamlining installation.
Enhanced Adhesion: Umbrella head and fishtail design promote strong grip and secure connections.
Ease of Use: Can be driven using a screwdriver or power drill.
Versatile Applications: Suitable for various materials, including wood, metal, and plastic.
Applications:
Joining components in construction, machinery, and vehicles.
Securing machine parts and equipment.
Installing door frames, signage, roofing panels, etc.
Repairing electronics and appliances.
2. Common Types of Self-Drilling Lag Screws
Pake Head Self-Drilling Lag Screws: These screws feature a pake head design for driving with a screwdriver.
Stainless Steel 304 Self-Drilling Lag Screws: Made from stainless steel 304, offering excellent resistance to chemical corrosion and rust. Their bright finish and mid-range price make them a popular choice.
Stainless Steel 201 Self-Drilling Lag Screws: These screws exhibit high hardness but lower corrosion resistance, suitable for dry, non-corrosive environments.
Stainless Steel 316 Self-Drilling Lag Screws: Considered the most durable and corrosion-resistant option, often used in shipbuilding, port construction, and chemical-handling machinery.
Self-Drilling Lag Screws for Metal Roofing: These screws come in various types, including umbrella head, SEC, and Dragon head designs. They feature a fishtail drill tip but have a hexagonal head. Unlike self-tapping screws, their hexagonal head incorporates a built-in washer to seal the hole and prevent water infiltration.
Self-Drilling Lag Screws for Wood: These screws are specifically designed for woodworking applications, joining wood components and securing them to wooden surfaces. They are typically used with larger, softer pre-drilled holes due to the absence of a built-in washer.
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