While there are many different types of bolts, most buyers really just want to know two things: what type of bolt do I need, and what size bolt should I buy? This guide has the answers.
Think of this as a buyer’s cheat sheet – practical and built for real-world projects. Get started by checking out the bolt types chart below, or jump to the section you need to see details on head style, sizing, uses and more for each bolt:
Here’s a quick summary of the most common bolt types you’ll encounter. Each listing shows the head type, common sizing, and best project uses so you can decide what fits your needs before diving into the details below.
| Bolt Type | Head Type | Common Sizing | Best For |
|---|---|---|---|
| Carriage Bolts | Smooth round head with square neck | 1/4"–3/4" diameter; 1"–10"+ length | Wood projects where a flush, snag-free surface is needed (decks, fences, furniture) |
| Hex Bolts | Six-sided hexagonal head | 1/4"–1" diameter; 1"–12"+ length | General construction, machinery, and furniture assembly |
| Lag Screws (Lag Bolts) | Large hex head with coarse threads | 1/4"–1/2" diameter; 1"–12"+ length | Heavy wood fastening like deck framing, posts, and outdoor structures |
| Tap Bolts | Hex head, fully threaded shaft | 1/4"–3/4" diameter; 1"–6"+ length | Equipment, automotive, and situations needing full-thread grip |
| Hanger Bolts | Headless, wood screw + machine threads | 1/4"–1/2" diameter; 1"–6" length | Furniture legs, wood-to-metal fastening, and concealed attachments |
| Hex Cap Screws | Hex head with washer face, precise fit | 1/4"–1" diameter; 1"–12"+ length | Machinery, automotive, and applications needing exact fit and torque |
| Sidewalk Bolts | Flat, low-profile head | 1/4"–3/8" diameter; 1"–6" length | Flush fastening into masonry, hurricane shutters, and smooth-finish installs |
What It Looks Like (Head Type): Smooth round head with a square neck beneath that locks into wood to prevent spinning
Common Sizing: Diameters from 1/4" to 3/4"; lengths from 1" to 10"+
Matching Hardware: Typically used with hex nuts and flat washers
Material & Finish Options: Zinc-plated for indoor projects; hot-dip galvanized or stainless steel for outdoor or deck applications
Buyer Tips: Drill a pilot hole that matches the square neck; best for projects needing a flush, snag-free surface such as furniture, decks, or playground equipment
Head Type Variations: Standard round head is most common; domed versions are sometimes used for decorative applications
Browse our full selection of carriage bolts. If you’d like more detail before buying, our carriage bolt guide covers common applications, how they’re installed, and how to choose the right size for your project.
Hex Bolt Head Type: Six-sided hexagonal head, the most recognizable bolt head style, designed for use with wrenches or sockets
Common Sizing: Diameters from 1/4" to 1"+; lengths from 1" to 12"+
Matching Hardware: Used with hex nuts, flat washers, and lock washers for stability
Material & Finish Options: Zinc-plated steel for indoor; hot-dip galvanized for outdoor; stainless steel for corrosion resistance; grade 5 or 8 alloy steel for high-strength applications
Buyer Tips: Use coarse threads for wood projects; fine threads for metal-to-metal fastening; always match bolt grade with nut grade
Head Type Variations: Standard hex head for general fastening; heavy hex head for structural strength; flange head with a built-in washer face for better load distribution
Browse our full selection of hex bolts. For a deeper dive into sizing and measurement, see our hex bolt size guide, which explains how to measure diameter, length, and threads per inch.
Lag Bolt Head Type: Large hex head with a thick, coarse-threaded shank designed to bite into wood
Common Sizing: Diameters from 1/4" to 1/2"; lengths from 1" to 12"+
Matching Hardware: Typically do not require nuts; often paired with washers for better load distribution
Material & Finish Options: Hot-dip galvanized or stainless steel for outdoor projects; zinc-plated for light-duty indoor applications
Buyer Tips: Pre-drill pilot holes to prevent splitting wood; ideal for heavy-duty fastening like deck framing, fence posts, and outdoor structures
Head Type Variations: Standard hex head is typical; some structural lag screws feature integrated washer or flange-style heads
Browse our full selection of lag screws. If you’d like to learn more before buying, our lag bolt guide explains the different types of lag bolts, sizing options, and thread considerations.
What It Looks Like (Head Type): Hex head with a fully threaded shaft, similar to hex bolts but threaded to the head
Common Sizing: Diameters from 1/4" to 3/4"; lengths from 1" to 6"+
Matching Hardware: Hex nuts, flat washers, and lock washers
Material & Finish Options: Zinc-plated or stainless steel for corrosion resistance; hardened steel for high-strength applications
Buyer Tips: Best when full thread engagement is needed, such as securing pulleys, motors, or equipment; not recommended where shear strength is the main requirement
Head Type Variations: Standard hex head only
Browse our full selection of tap bolts.
Hanger Bolts: Headless design with wood screw threads on one end and machine screw threads on the other
Common Sizing: Diameters from 1/4" to 1/2"; lengths from 1" to 6"
Matching Hardware: Machine-threaded end pairs with nuts, couplers, or threaded inserts
Material & Finish Options: Zinc-plated for indoor projects; stainless steel or galvanized for outdoor use
Buyer Tips: Install with a driver tool or double-nut method; commonly used for furniture legs, wood-to-metal fastening, or concealed attachments
Head Type Variations: None (headless design)
Browse our full selection of hanger bolts.
Hex Cap Bolt Head Types: Hexagonal head with a precise washer face under the head, manufactured to tighter tolerances than standard hex bolts
Common Sizing: Diameters from 1/4" to 1"+; lengths from 1" to 12"+
Matching Hardware: Hex nuts, flat washers, and lock washers
Material & Finish Options: Alloy steel for strength; zinc-plated or stainless steel for corrosion resistance
Buyer Tips: Ideal where alignment, torque, and precision are critical; often used in machinery and automotive applications; commonly confused with hex bolts but designed for more exact fit
Head Type Variations: Standard hex head; heavy hex head for higher strength
Browse our full selection of hex cap bolts.
Sidewalk Bolt Head Type: Flat, low-profile head with machine screw threading designed to sit flush with the surface
Common Sizing: Diameters from 1/4" to 3/8"; lengths from 1" to 6"
Matching Hardware: Often used with anchors or pre-threaded inserts; may pair with washers depending on application
Material & Finish Options: Stainless steel for high moisture or coastal environments; zinc-plated for indoor or light-duty use
Buyer Tips: Commonly used for hurricane shutters, masonry fastening, and other applications needing a flush surface; choose stainless steel when durability outdoors is a priority
Head Type Variations: Flat head is standard; some versions available with countersunk styles
Browse our full selection of sidewalk bolts. If you’re installing hurricane shutter panels, our hurricane shutter hardware guide explains all the fasteners and accessories you’ll need for a complete, secure setup.
Bolt size depends on the material you’re fastening and how much load it needs to handle. Length is typically measured from under the head (except countersunk bolts, which include the head in the measurement). Diameter is the thickness of the shank, and threads can be coarse (better for wood) or fine (better for metal).
For a detailed breakdown, including common sizing charts and how to measure bolts correctly, see our bolt size chart.
A bolt’s finish determines how well the bolt will resist corrosion and last in different environments:
Plain Steel: For indoor use; prone to rust outdoors.
Zinc-Plated: Provides basic rust resistance; good for general-purpose use.
Hot-Dip Galvanized: Thick protective coating for outdoor and pressure-treated lumber projects.
Stainless Steel: Excellent corrosion resistance; best for outdoor, coastal, and marine projects.
Black Oxide: Smooth black appearance with mild corrosion resistance.
Choose your finish based on where the bolt will be used and how long you need it to last.
Bolt grades measure strength. A higher grade means the bolt can handle greater stress:
Grade 2: Standard, low-to-medium strength; fine for light-duty, indoor applications.
Grade 5: Medium strength; common in construction and automotive.
Grade 8: High strength; used in heavy equipment, structural applications, and demanding load conditions.
For outdoor durability, consider both grade and finish (e.g., Grade 5 galvanized vs. stainless).
Think about these buyer basics before you purchase:
Project Type: Are you fastening wood, metal, or concrete?
Environment: Indoor vs. outdoor use; dry vs. high-moisture or coastal.
Load Strength: Light-duty (furniture) vs. heavy-duty (decks, machinery).
Tools On Hand: Wrench, socket, screwdriver, or drill requirements.
Head Style Preference: Flush (carriage/sidewalk) vs. protruding (hex/lag) vs. decorative.
The most common bolt head styles you’ll encounter include:
Hex Head: Six-sided, versatile, easy to install with wrenches.
Round Head: Smooth, low-profile, often used in furniture or outdoor wood projects.
Flat (countersunk) Head: Designed to sit flush with the surface.
Domed/Cap Head: Decorative and protective, covering exposed threads.
Socket/Allen Head: Recessed hex drive, great for tight spaces or precision fastening.
Head style affects not just appearance but also the tools you’ll need and how the bolt sits in your finished project.
Whether you’re fastening deck framing, assembling furniture, or securing hurricane shutters, the right bolt makes all the difference in strength, safety, and durability. At The Fastener Depot, we stock the bolt types, finishes, and sizes you need — backed by personal service and practical advice you can count on.
If you’re not sure which bolt is best for your project, our team is here to help. We’ll guide you through head styles, sizes, and finishes so you can buy with confidence.
Browse our full selection of bolts or reach out to us directly for quick, friendly support.
