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Fasteners and Fastening Systems Reference

Reference Equipment Updated Jul 24, 2026 · HVAC · Plumbing · Electrical · Roofing · Garage Door

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 (lead anchor): brass sleeve with spreading legs; older technology. 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

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

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