Complete Screw Size Chart and Selection Reference Guide

Selecting the right screw for the job is all about understanding the diameter, thread pitch, and specific application requirements needed to get the job done in a timely manner while maintaining code compliance and a safe structure. Whether you're hanging drywall, framing a deck, or securing electrical boxes, this guide breaks down screw specifications and applications for jobsite readiness. 

US screws follow this format: Diameter - Threads Per Inch × Length

Example: ¼-20 × 2" means:

• ¼ inch diameter
• 20 threads per inch (coarse thread)
• 2 inches long

Metric screws use: M(Diameter) × Pitch × Length

Example: M6×1.0×30mm means:

• 6mm diameter
• 1.0mm thread pitch
• 30mm long

Diameter: Width of the screw shank (#8 = 0.164", #10 = 0.190")

Thread Count/Pitch: Thread density (US uses TPI, metric uses mm between threads)

Length: Measured from under the head to tip

UNF (Unified National Fine) threads are built for strength and precision. With more threads per inch than UNC, they lock in tighter, hold stronger, and resist vibration better. That’s why you’ll see them in places where failure isn’t an option, like for engine bolts, aircraft fasteners, hydraulic fittings, and precision machinery. Designed with a 60° thread angle, UNF fasteners give you a secure fit and reliable clamping force when the job demands durability and accuracy.

• Fewer, deeper threads per inch
• Faster installation - threads engage quickly
• Better for soft materials - wood, plastic, drywall
• More forgiving - tolerates debris and minor damage
• Standard for construction - framing, decking, general carpentry

• More, shallower threads per inch
• Higher tensile strength - more threads engaged
• Better vibration resistance - automotive, machinery applications
• Precision applications - where exact fit matters
• Thinner materials - sheet metal, precision assemblies

Example: A ¼" bolt comes as ¼-20 UNC (coarse) or ¼-28 UNF (fine). Construction typically uses UNC; machinery uses UNF.

• Design: Tapered body, coarse threads, often partially smooth shank
• Purpose: Pull materials together tightly
• Sizes: #6-#10, lengths 1"-3"
• Heads: Flat (countersunk), round, or pan

Best for: General carpentry, furniture, trim work

Design: Bugle head prevents paper tearing

Two main types:

• W-type (coarse thread): Wood studs - drives fast, holds strong
• S-type (fine thread): Metal studs - self-drilling point

Common sizes: #6 or #8, 1¼"-2" long
Coating: Black phosphate for corrosion resistance

• Design: Fully threaded, sharp point, fine threads 
• Purpose: Self-tap into thin metal or plastic
• Heads: Pan, round, hex washer
• Sizes: #8-#14 typical

Applications: HVAC ductwork, metal panels, electrical boxes

Design: Uniform diameter, precise threads, blunt end
Purpose: Use with nuts or tapped holes
Drives: Phillips, slotted, hex socket, Torx

Common applications:

• #6-32: Electronics, light fixtures
• #8-32: Electrical boxes, heavy fixtures
• #10-32: Ceiling fans, ground screws

• Design: Heavy-duty wood screws with hex or square heads
• Sizes: ¼" to ⅝" diameter, 2"-12" long
• Strength: Highest holding power for wood connections
• Installation: Requires a pre-drilled pilot hole and a wrench

Applications:

• Deck ledger boards
• Beam connections
• Retaining walls
• Structural framing

Example: ½"×5" hex-head lag bolt for ledger to rim joist connection

• Design: Built-in drill bit tip eliminates pilot holes
• Types: #2, #3, #4 drill points for different metal thicknesses
• Applications: Metal roofing, steel framing, HVAC ductwork

Advantage: One-step installation - drill and tap simultaneously

• Design: Hardened steel, aggressive threads for masonry
• Sizes: 3/16" to ½" diameter
  Installation: Drill hole with carbide bit, drive screw
• Coating: Blue coating or galvanized for corrosion resistance

Applications:

• Mounting electrical boxes to concrete
• Furring strips on masonry walls
• Conduit and pipe supports

• Phillips (#1, #2, #3): Most common, good for light-duty applications
• Robertson (Square): Popular in construction, less cam-out than Phillips
• Torx (T15, T20, T25, T30): High torque applications, deck screws, structural fasteners
• Hex Socket (Allen): Machine screws, high-precision applications

• Impact drivers: 18V-20V cordless for high-volume screw driving
• Bit quality: Impact-rated bits (Milwaukee SHOCKWAVE, Makita Gold) resist cam-out
• Magnetic holders: Keep bits secure during overhead work
• Bit sets: Comprehensive sets with common sizes for each trade

• Interior applications: Standard zinc coating sufficient
• Exterior/wet locations: Stainless steel or hot-dip galvanized
• Pressure-treated lumber: Use compatible coatings to prevent reaction
• Marine environments: 316 stainless steel minimum

Shear loads: Diameter matters most - use larger screws

Tension loads: Thread engagement matters - ensure adequate depth

Dynamic loads: Fine threads resist vibration loosening better

Residential framing: #10 × 3" wood screws, ½" lag screws for connections

Drywall installation: #6 drywall screws (W-type wood, S-type metal studs)

Electrical rough-in: #6-32 and #8-32 machine screws, #8 sheet metal screws

HVAC installation: #8 sheet metal screws, self-drilling for metal ductwork

Concrete work: ¼" Tapcon screws with matching carbide bits

Thin sheet metal (22-26 gauge): #8 self-drilling screws

Standard lumber (2x material): #8-#10 wood screws

Engineered lumber: Manufacturer-specified structural screws

Masonry/concrete: Match screw diameter to required holding power

1. Pre-drilling: Always pre-drill for lag screws and when working near board edges
2. Torque control: Use appropriate torque settings to prevent over-driving
3. Thread engagement: Minimum 6 full threads in the receiving material
4. Pilot holes: Required for hardwoods and large screws to prevent splitting
5. Bit maintenance: Replace worn bits immediately - they cause more damage than they're worth

1. Wrong thread type: Using fine threads in soft materials (over-complicates installation)
2. Insufficient engagement: Too-short screws for the application
3. Over-torquing: Strips threads or breaks screw heads
4. Wrong coating: Using incompatible metals that cause galvanic corrosion
5. Improper pilot holes: Too large (no holding power) or too small (splits material)

Understanding the relationship between fastener cost and performance helps make informed decisions about when to specify premium fasteners versus standard options.

Standard zinc-plated screws work well for interior applications and offer the lowest initial cost. However, they're unsuitable for exterior use and may require replacement sooner in demanding applications. For high-volume interior work, standard screws provide adequate performance at minimal cost.

Stainless steel screws cost 3-5 times more than zinc-plated screws but offer superior corrosion resistance and longer service life. In exterior applications or corrosive environments, the higher initial cost is offset by eliminated replacement costs and improved reliability.

Specialty coatings like ceramic or polymer coatings provide enhanced performance for specific applications. While expensive, they may be cost-effective for high-value installations or when service access is difficult.

Modern construction faces increasing environmental and regulatory requirements that affect fastener selection. Lead-free coatings are now required in many applications, particularly those involving potable water systems. Recycled content requirements may specify certain fastener materials or coatings.

Green building standards often require documentation of fastener materials and coatings. Some programs award points for using recycled content fasteners or those with low environmental impact coatings. Understanding these requirements helps in specification and procurement.

Building codes specify minimum fastener requirements for structural applications. These requirements include material grades, corrosion resistance levels, and installation methods. Always verify that selected fasteners meet code requirements for the specific application.

Picking the right screw isn’t guesswork—it’s about knowing your sizes, thread types, and the job at hand. Whether you’re driving lag screws into a ledger board, hanging drywall, or bolting machinery together, the right fastener makes the difference between a quick fix and a long-lasting connection. Use this chart as a reference, keep your materials in mind, and don’t cut corners on quality. The right screw saves time, prevents callbacks, and keeps your work standing strong.