Fasteners and Fastening Systems Reference

Why this matters

Every install fastens something to something else. Wrong fastener = wrong holding power, premature failure, or a code violation. The fastener world is broad - screws, bolts, nails, anchors, structural connectors - and each has a right and wrong application. Knowing the basics keeps the install solid and the inspection clean.

Wood screws

Standard wood screw: flat head (countersinks below surface), tapered shank, partially threaded. Comes in #6 (small) to #14 (large) sizes; lengths 1/2" to 6"+. Use for joining wood-to-wood.

Drywall screw: black phosphate-coated, bugle-head (self-countersinks slightly), fine or coarse thread. For attaching drywall to studs (NOT for structural use - brittle, snaps under shear load).

Deck screw: stainless or coated weather-resistant, sharp point, often #8 or #10. For exterior decks; rated for ground-contact treated lumber.

Cabinet screw / pan-head: flat washer-style head sits on the surface. For attaching cabinet boxes to studs.

Construction screw / structural screw (GRK RSS, Spax PowerLag, Simpson SDS): engineered for structural use; replaces lag bolts in many applications. Star-drive head (T-25 or T-30). Higher shear and pullout values than standard wood screws. Always check the manufacturer's load rating.

Lag bolts / lag screws

• Heavy-duty wood-to-wood fastener
• Hex head, requires socket or wrench to drive
• Sizes: 1/4", 5/16", 3/8", 1/2"
• Use for: hanging beams, posts, heavy hardware
• Pilot hole required - pre-drill at root diameter of the thread (e.g., 1/4" lag = 5/32" pilot in softwood, 11/64" in hardwood)
• Often being replaced by structural screws (easier install, no pilot in many cases)

Machine screws and bolts

• Machine screw: threaded for full length, head varies (flat, pan, round, button). Used with a nut or threaded receiver. #4 to #12 in small sizes; 1/4-20 and up in fractional.
• Cap screw (hex bolt): larger, threaded into a threaded hole or used with a nut. 1/4" to 1+ inch diameter.
• Socket cap screw (Allen head): Allen wrench drive; precision applications.
• Threaded rod (allthread): rod threaded along its length; cut to need, used with nuts at both ends.

Thread types:

• UNC (Unified National Coarse): standard, e.g., 1/4-20 (1/4" diameter, 20 threads per inch)
• UNF (Unified National Fine): finer thread, more threads per inch - e.g., 1/4-28
• Metric: M6×1.0 (6 mm diameter, 1.0 mm thread pitch)

Don't mix UNC, UNF, and metric - threads won't mate.

Sheet metal screws (TEK screws, self-drilling)

• Hardened tip designed to drill its own pilot
• Hex head most common (for nut driver), but Phillips and square also available
• Used for: HVAC duct connections, metal roofing, automotive
• #8 through #14 typical sizes
• #1 point for thin metal (<0.040"), #3 point for thicker (up to 0.187"), #5 point for heavy structural

Nails

• Common nail: smooth shank, sized by penny (d) - 6d (2"), 8d (2-1/2"), 10d (3"), 16d (3-1/2"), 20d (4")
• Sinkers: thinner than common, vinyl-coated, easier driving
• Box nails: thinner shank than common
• Ring-shank or screw-shank: more holding power
• Roofing nail: large head, short shank - 1" to 1-3/4"
• Finishing nail: small head, sets below surface - for trim
• Cap nail: large plastic cap; for housewrap and felt paper

Nail vs screw choice:

• Nail: faster, better in shear (perpendicular load); standard framing
• Screw: better in pullout; better when material will swell/shrink (slamming nails loose); use for plywood subfloor, drywall, exterior trim

Wall anchors (hollow walls)

Plastic expansion anchor: small plastic sleeve that expands when screw is driven. Light-duty only (1-5 lb).

Toggle bolt: spring-wing or plastic toggle that opens behind the drywall. Medium-heavy duty (20-100 lb depending on wall). Requires larger hole.

Snap-toggle (Toggler): plastic strap-mounted toggle; faster install than wire toggle; medium-heavy duty.

Self-drilling plastic anchor (E-Z Ancor, ZipIt): screws directly into drywall, then accepts the mounting screw. Light-medium duty (10-30 lb).

Molly bolt (hollow-wall sleeve anchor): a slotted steel sleeve whose legs collapse and spread flat against the back of the board as the screw is tightened; older technology, and not to be confused with the lead expansion anchor listed under masonry below. 5-25 lb.

Concrete and masonry anchors

Plastic sleeve anchor: small, light-duty (5-30 lb in concrete). Predrilled hole, plastic sleeve, then screw spreads sleeve.

Wedge anchor (Red Head, Powers): threaded stud with a clip at the end that wedges against the hole. Heavy duty (100-1000+ lb depending on size). Hole drilled with masonry bit, anchor inserted, nut tightened to wedge.

Sleeve anchor: similar to wedge but spreads a sleeve outward; smaller hole-to-stud ratio. Medium-heavy duty.

Drop-in anchor: internally-threaded brass sleeve set into a hole; threaded rod or bolt screws into it. Used where the bolt may need to be removed.

Tapcon (concrete screw): self-tapping concrete screw - drills its own pilot in masonry with the right bit. Light-medium duty (50-200 lb depending on size and embedment).

Lead expansion anchor: older, less common today; lead sleeve expands when screw is driven.

Adhesive anchor (epoxy): chemical bond. Highest holding capacity. Requires hole-clean, epoxy injection, then anchor inserted. For seismic / structural applications.

Structural connectors (Simpson Strong-Tie and equivalents)

Code-listed metal hardware for wood-frame structural connections:

• Joist hangers (LUS, LSSU, U series) - hang one joist from another or from a beam
• Hurricane ties / rafter ties (H1, H2.5, H10) - connect rafters to top plate
• Strap ties (LSTA, MSTA) - tie connections across joints
• Holdowns (HDU, PHD) - connect framing to foundation
• Beam-to-post connectors (CC, CCQ, ECC) - column-cap or column-bottom connectors

Fastening: use only the manufacturer-specified fasteners. Often 10d×1-1/2" common nails for hangers (NOT roofing nails - too short shank). Some require structural screws.

Torque values (common applications)

• Standard wall outlet / switch terminal screws: 12-15 in-lb
• Service panel breakers: 18-25 in-lb (small breakers), 25-35 in-lb (larger), per manufacturer torque tag
• Service entrance lugs: 150-275 in-lb (per panel manufacturer)
• Standard 1/4" hex lag in wood: 100-150 in-lb (hand-tight + quarter turn typical)
• Pipe flange bolts: depends on flange class and gasket; consult chart

Always check the manufacturer's torque spec. Loose connections cause heat and resistance; over-torqued connections strip or break.

Choosing the right fastener

Five questions, in order. Answer them and the fastener picks itself.

1. What is the base material? Wood, steel stud, sheet metal, solid masonry, hollow block, poured concrete, drywall alone, tile over backer. This eliminates most of the catalog immediately. Nothing that relies on thread bite in wood will hold in a hollow wall, and no drywall anchor belongs in concrete.

2. Which direction is the load? Shear (across the fastener) or tension and pullout (straight out). Nails are strong in shear and weak in withdrawal. Screws are the reverse. Anything overhead, anything hanging, anything a body could pull on is a tension load and needs pullout capacity, not just a fastener that goes in.

3. How much load, and is it static or cycling? A cycling load (a door slamming, a compressor vibrating, a garage door spring) loosens fasteners that would hold a dead weight forever. Cycling loads want a through-bolt, a locking arrangement, or a fastener rated for the duty, not a wood screw that will wallow its hole.

4. Is the connection structural or code-listed? If it carries structure, the fastener is specified, not chosen. Structural connectors require the manufacturer's stated fastener in every hole. Substituting a shorter or thinner nail, or leaving holes empty, voids the rated capacity even though the hardware looks installed. Same for anchors under an evaluation report; the report specifies embedment, edge distance, spacing, and hole size.

5. What is the environment? Exterior, wet, or in contact with treated lumber means the coating matters. Treated lumber chemistry eats bare and lightly plated steel; use hot-dip galvanized or stainless rated for the application. Mixing dissimilar metals in a wet location sets up galvanic corrosion, so match the fastener to the flashing, the hanger, and the connector it touches.

Then check the fit:

• Length: enough thread engagement in the second material, not the first. A rule of thumb for wood is at least half the fastener in the receiving member.
• Pilot hole: required for lags and for anything near an edge or end of a board. Splitting the wood removes the holding power you just paid for.
• Head style: does it need to countersink, sit proud on a washer, or bear on a surface without crushing it.
• Edge distance and spacing: too close to an edge in concrete cracks the substrate; too close in wood splits it.

The failures this prevents: drywall screws used structurally (brittle, snap in shear), roofing nails in a joist hanger (shank too short to develop capacity), a hollow-wall anchor in a hollow block face shell, an anchor set in a hole drilled with a worn bit, and a treated-lumber deck ledger fastened with plain steel that rusts through in a few seasons.

When you are unsure: pick the fastener the manufacturer of the thing you are hanging specifies. That spec exists because someone tested it, and following it moves the liability off you.

References

• Simpson Strong-Tie catalog and connector load tables
• GRK Fasteners and Spax PowerLag technical guides
• IRC R301 (structural connection requirements)
• ICC-ES Evaluation Service Reports (ESR) for code-listed structural fasteners
• NER (National Evaluation Reports) for anchors and fasteners