Screws & Bolts
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What Are Screws and Bolts?
Screws and bolts are threaded fasteners used to clamp parts together. In general terms, a bolt is used with a nut (or a tapped component) and is tightened by the nut, while a screw forms or engages threads in the material or a pre-tapped hole and is tightened at the head. The right choice depends on the joint design, access, required strength, and environment.
Common Types of Screws & Bolts
- Deck & Wood Screws – Coated or stainless for exterior lumber; sharp wood threads for pull-out resistance.
- Machine Screws – Uniform machine threads for tapped holes or nuts; pan, flat, button, and socket heads.
- Hex Head Bolts / Cap Screws – General assembly and structural use; available in SAE grades and metric property classes.
- Lag Bolts (Lag Screws) – Heavy-duty wood-to-wood or wood-to-masonry connections.
- Socket Head Cap Screws – Internal-hex drive for machinery, fixtures, and tight clearances.
- Set Screws – Headless screws that lock collars, pulleys, and shafts (cup, cone, flat, dog points).
- Roofing Screws – Self-sealing washers for metal roofing and siding.
- Hanger Bolts & Dowel Screws – Wood thread on one end, machine thread on the other for mounting studs and hardware.
Materials & Finishes
- Stainless Steel (304/18-8) – General corrosion resistance; 316 for marine/coastal or chemical splash.
- Carbon Steel, Zinc Plated – Economical indoor protection.
- Hot-Dip Galvanized – Thick zinc layer for harsh outdoor exposure and treated lumber hardware.
- Silicon Bronze & Brass – Non-magnetic, good corrosion resistance; common in marine/architectural work.
- Coated Exterior Screws – Polymer/ceramic coatings formulated for deck framing and outdoor projects.
Threads, Grades & Strength
- Coarse (UNC) vs. Fine (UNF) – Coarse assembles quickly and holds well in softer materials; fine offers higher tensile capacity and better adjustment in hard materials.
- SAE Grades – Grade 2 (general), Grade 5 (medium/high strength), Grade 8 (high strength). Metric equivalents: 8.8, 10.9, 12.9.
- Wood / Tapping Threads – Deep, spaced threads for timber and sheet metals; self-drilling points eliminate pre-drilling in thin metals.
Head & Drive Styles
- Head – Hex, socket (internal hex), pan, button, flat/countersunk, truss, flanged.
- Drive – Phillips, square, internal-hex (Allen), slotted, and star drive (generic). Choose a drive that matches your tools and access.
How to Choose the Right Fastener
- Define the joint – Nut-and-bolt clamp, tapped hole, or direct wood fastening.
- Match material to environment – Stainless or hot-dip galvanized for outdoors; coated deck screws for treated lumber; zinc plated for dry interior use.
- Select diameter & length – Diameter for strength and thread engagement; length to pass through materials and fully seat with washers if used.
- Pick thread & grade – Coarse vs. fine; choose the grade/property class that meets load requirements.
- Choose head & drive – Based on clearance, appearance, tool access, and needed clamping area.
Sizing & Fit
- Measuring length – From the bearing surface under the head to the tip (except countersunk heads, which measure overall).
- Thread pitch – Imperial (TPI) vs. metric (mm pitch). Ensure the nut or tapped hole matches.
- Pilot holes – Wood screws and lag bolts require a pilot sized near the root diameter to prevent splitting and ensure proper torque.
- Washers & spacers – Use flat and lock washers as specified to distribute load and help resist loosening.
Corrosion & Compatibility
- Avoid mixing dissimilar metals in wet or coastal environments (e.g., copper with plain steel) to reduce galvanic corrosion.
- For treated lumber, use hot-dip galvanized or stainless fasteners and hardware rated for the preservative chemistry.
Installation Tips
- Use the correct driver size; apply steady pressure to prevent cam-out and head damage.
- Tighten in stages and in a cross pattern where applicable to seat parts evenly.
- Verify torque or snug-tight requirements from your design/spec; re-check high-vibration joints with mechanical locking where needed.
Practical Selection Examples
Decking & Outdoor Framing
Coated deck screws or stainless (304 for most builds, 316 near salt or pool water). Lag bolts for ledger and heavy connections where code allows.
Machinery & Fixtures
Socket head cap screws (metric 12.9 or SAE Grade 8 when specified) with fine threads in hard materials; set screws for collars and pulleys.
Roofing & Exterior Panels
Self-drilling roofing screws with sealing washers sized to the panel and purlin thickness; hot-dip galvanized or stainless in corrosive atmospheres.
Frequently Asked Questions About Screws and Bolts
While both screws and bolts are threaded fasteners, they have distinct characteristics. Screws typically have a tapered shank and are designed to create their own threads in materials like wood or plastic. Bolts, on the other hand, usually have an unthreaded shank and require a nut to secure them in place.
Selecting the appropriate fastener depends on the materials you're working with, the required holding strength, and the environmental conditions. Consider factors such as the screw or bolt's size, thread type, material, and finish. If you're unsure, our knowledgeable staff can help you make the right choice.
Bolts and screws come in a wide range of sizes to suit various applications. Some of the most common diameters include #8, #10, 1/4", 5/16", and 3/8". Length requirements vary depending on the project, with options typically ranging from 1/2" to several inches.
Screws and bolts are available in different materials to meet specific needs. Steel is the most common choice, offering strength and affordability. Stainless steel provides corrosion resistance, while brass and bronze are often used for decorative purposes. Other materials include aluminum, nylon, and silicon bronze.
The head type determines the tool required for installation. Common head types include Phillips, flat, hex, and socket cap. Some specialty fasteners, like self-drillers, have unique head designs for specific applications.
The fastener should be long enough to fully engage the threads in the material without protruding excessively. For wood projects, a good rule of thumb is to choose a length that allows the fastener to penetrate about two-thirds of the material's thickness.
When working on outdoor projects, it's crucial to choose fasteners that can withstand exposure to the elements. Opt for screws and bolts with rust-resistant coatings like galvanized, zinc-plated, or stainless steel to ensure lasting durability.
Using the appropriate tools is key to efficiently driving screws and bolts. For most applications, a screwdriver or drill with the correct bit will suffice. Hex head bolts require a wrench or socket set. Always ensure the tool properly fits the fastener head to avoid damaging the screw or bolt.
To keep screws and bolts secure, consider using thread-locking compounds, lock washers, or lock nuts. These methods help prevent vibration and other forces from causing the fasteners to loosen, ensuring a long-lasting, stable connection.
If a screw or bolt proves challenging to remove, start by applying a penetrating oil to help loosen any rust or debris. For stubborn fasteners, using a manual impact driver can help. In some cases, applying heat to the surrounding area may cause the material to expand slightly, making removal easier. If all else fails, carefully extracting the damaged screw or bolt may be necessary.
Use coated deck screws or stainless steel (304 for most projects, 316 for coastal/pool environments) to resist corrosion.
Both resist corrosion, but in different ways. Hot-dip galvanized offers thick zinc protection for rugged weathering; stainless resists rust via alloy chemistry and is ideal around moisture, salt, or chemicals.
Grade 2 is light duty, Grade 5 is medium/high strength, and Grade 8 is high strength. Match grade to load and safety requirements.
Coarse threads assemble quickly and hold better in softer materials; fine threads provide higher tensile capacity and better adjustment in hard materials.
Use the manufacturer’s table for diameter and species; as a rule, pilot holes are slightly smaller than the screw’s root diameter so the threads bite without splitting. (General best practice based on retailer/guide tables.)
Avoid mixing dissimilar metals in wet or coastal environments to reduce galvanic corrosion; keep materials compatible when possible.