Fasteners and Hardware: Practice Questions & Explanations

Screw types and characteristics: WOOD SCREWS have tapered point; threads typically only on part of shank (smooth shank near head); coarse threads cut their own path in wood; for connecting wood pieces; HEAD TYPES: flat (for countersinking), oval, round, pan; slot, Phillips, square (Robertson), star (Torx) drives; sizes by gauge (#4 small to #14 large) and length (1/2 inch to 4 inches typical). MACHINE SCREWS have uniform threads along entire shank; flat tip (or near-flat); designed to fit into a nut or pre-threaded hole; precise thread fit; used in machinery, electronics, fixtures; head types include pan, round, flat, oval, hex (cap), fillister, button; sizes by diameter and threads-per-inch (e.g., #6-32 = #6 gauge, 32 TPI) or metric (M3, M4, M5, M6, M8, M10 = diameter in mm). SHEET METAL SCREWS are like wood screws but designed for thin metal; threads cut into metal; self-drilling types have drill-point tip eliminating need for pilot hole. DECK SCREWS are wood screws specifically for deck construction; corrosion-resistant coating (galvanized, ceramic-coated, stainless); often square or torx drive for power-driver use. DRYWALL SCREWS have bugle-head for flush installation; coarse-thread for wood studs, fine-thread for metal studs; black phosphate coating; brittle (don't use as structural fasteners). LAG SCREWS or LAG BOLTS are large heavy-duty wood screws with hex heads; for heavy applications like deck framing, attaching beams; predrill pilot hole; install with wrench or socket. SELF-TAPPING SCREWS cut their own threads in metal; not as strong as machine screws in tapped holes but faster installation. CONCRETE SCREWS (Tapcon) are for screwing into concrete after drilling pilot hole; blue-coated typically. THREAD DESIGNATIONS SAE: #6-32, #8-32, #10-24, #10-32, 1/4-20, 1/4-28, 5/16-18, 3/8-16, 1/2-13; the second number is TPI. METRIC: M3-0.5, M4-0.7, M5-0.8, M6-1.0, M8-1.25, M10-1.5; the second number is thread pitch (mm between threads). PILOT HOLES for wood are typically 70-80 percent of screw root diameter; CLEARANCE HOLE in top piece (larger, equal to screw shank) lets it pass through cleanly while threads bite into bottom piece; COUNTERSINK to recess head flush. WASHERS distribute load, prevent damage to material; flat washers for general use; lock washers (split-ring, star, etc.) prevent loosening from vibration; fender washers are large-diameter for soft materials. BOLT vs SCREW distinction: bolts are used with nuts; screws thread into the material itself. NUTS: hex (most common), castle (with slots for cotter pin), lock nut (nyloc has nylon insert, jam nut, all-metal locking), wing nut (finger-tightened). NAIL TYPES: common (full-diameter, for framing), box (thinner, for finish), finish (small head, for trim), casing, brads (very small), roofing (wide head), masonry (hardened). Nail sizes by 'd' (penny): 8d = 2-1/2 inch common framing; 16d = 3-1/2 inch common framing.

Washer functions: DISTRIBUTE LOAD (spreads clamping force over larger area; prevents bolt head/nut from sinking into softer materials like wood, plastic, aluminum, painted steel; without washer, point loading can crush material); PREVENT SURFACE DAMAGE (protects finish from being marred by rotation of bolt/nut during tightening); PROVIDE BEARING SURFACE (clean smooth surface for nut to bear against; especially important on rough surfaces); PREVENT LOOSENING (lock washers add vibration resistance); FILL SPACE (when bolt is too long, washers or spacers take up the difference); ELECTRICAL ISOLATION (special washers like nylon, fiber electrically isolate parts). WASHER TYPES: FLAT WASHER is standard, round, flat, for general load distribution. FENDER WASHER has large outer diameter for soft materials, thin sheet metal, distributing load over wide area; common in automotive body panels. LOCK WASHER prevents nut loosening from vibration; types: SPLIT-RING (helical spring, most common; one end of split twists creating friction and bite into surface), STAR (TOOTH, external or internal teeth bite into surfaces), DOUBLE-COIL; modern bolted joints often use Nord-Lock washers (wedge-locking, very effective), prevailing-torque nuts (Nyloc with nylon insert), or thread-locking compound (Loctite). BELLEVILLE WASHER (conical spring) provides constant spring force for high-vibration applications. SHOULDER or DOUBLE-D WASHER has special shape for specific applications. SEALING WASHER has bonded rubber to seal against fluid leaks; common in plumbing, hoses, oil drain plugs. WAVE or CRESCENT WASHER has wavy form with mild spring tension. WASHER MATERIALS: zinc-plated steel (common, rust-resistant for indoor use); stainless steel (corrosion-resistant for outdoor, marine); brass (non-magnetic, decorative); nylon/plastic (non-conductive, light); rubber (sealing, vibration damping); bonded (rubber-to-metal for sealing under pressure); copper (sealing on certain mating surfaces). INSTALLATION ORDER (typical): bolt head, flat washer, material, material, flat washer, lock washer, nut. Lock washer goes against the nut (or rotating element); flat washer between material and lock washer to protect material. CRITICAL applications use torque wrench to apply specified torque; under-tight equals clamping force insufficient; over-tight equals bolt stretches or breaks. Some assemblies use STRETCH BOLTS or TORQUE-TO-YIELD (TTY) bolts where measured rotation past initial torque deliberately stretches bolt to a specific clamp load; one-time-use, must be replaced. THREAD ENGAGEMENT rule of thumb: 1.5 times bolt diameter of thread engagement for normal applications; 2 times or more for aluminum or other softer materials; thread engagement past full threads of nut doesn't add strength.

NAIL SIZES are designated by 'd' (penny). The 'd' abbreviation comes from the Latin DENARIUS (a Roman coin) because early nails were sold by their cost in pennies per hundred. Common nail sizes (length in inches): 2d equals 1 inch; 3d equals 1.25 inch; 4d equals 1.5 inch; 6d equals 2 inches; 8d equals 2.5 inches; 10d equals 3 inches; 12d equals 3.25 inches; 16d equals 3.5 inches; 20d equals 4 inches; 30d equals 4.5 inches; 40d equals 5 inches; 50d equals 5.5 inches; 60d equals 6 inches. Most commonly used in framing: 8d for sheathing, 16d for framing studs to plates. The penny designation is for length only. NAIL TYPES AND APPLICATIONS: COMMON NAILS have full-diameter shaft and flat head; for framing and general construction; sturdy, hold well. BOX NAILS are thinner than common nails of same length; less likely to split wood; for siding, fencing, sheathing. FINISH NAILS have small unobtrusive head (cup-shaped); for trim, cabinets where you don't want the head to show; head countersunk slightly below surface, filled with putty. CASING NAILS are larger than finish nails with slightly larger head; for window/door casing. BRADS are very small finish nails (18 or 23 gauge); for small trim, picture frames; usually shot from brad nailer (pneumatic). ROOFING NAILS have wide flat head; galvanized for rust resistance; for shingles, felt paper; sized 7/8, 1, 1-1/4 inch; head pulls into shingle to hold. DRYWALL NAILS have bugle head, ringed shank for grip in framing through drywall; alternative to drywall screws. MASONRY NAILS are hardened steel for nailing into concrete/brick. DECK NAILS are galvanized or stainless for outdoor use; corrosion-resistant; ringed or spiral shanks for better grip. SPIRAL/RINGED SHANK NAILS are twisted or with rings; better holding power; especially for siding, decking, framing in seismic/wind zones (resist withdrawal). MATERIALS: STEEL is bright (uncoated, indoor only — rust), galvanized (zinc-coated, outdoor/treated wood), stainless steel (premium outdoor); ALUMINUM is for aluminum siding (no galvanic corrosion); COPPER for copper roofing; BRASS decorative. NAIL HEADS: full-size flat heads hold larger area (for plywood, sheathing); checked heads (cross-hatching) for grip; bugle head for drywall; convex/cup heads for finish nails; no head for double-headed nails (for temporary construction; pull out easily). NAIL GUNS (PNEUMATIC NAILERS): use compressed air to drive nails; types: FRAMING NAILER (driving 16d framing nails), FINISH NAILER (15 or 16 gauge for trim), BRAD NAILER (18 or 23 gauge for small trim), ROOFING NAILER (coil-fed for roofing nails), SIDING NAILER (galvanized box nails for siding). Battery-powered cordless options also available. SAFETY: never point at people; never carry with finger on trigger; wear safety glasses (ricochet hazard); use SEQUENTIAL TRIP (not bump-fire) for accuracy; bump-fire can cause double-fires when accidentally striking. NAIL vs SCREW: nails install faster (especially with nail gun); better in shear (sideways forces) which makes them good for framing; cheaper; screws have superior pull-out resistance, slower installation, more secure for things expected to be disassembled.

TORQUE SPECIFICATIONS exist because fastener clamping force is critical for both safety and function. UNDER-TIGHTENING risks: bolts loosen from vibration; joint opens; fluids leak; structural failure. OVER-TIGHTENING risks: bolt stretches beyond yield point (permanent deformation); threads strip in softer material (aluminum, plastic); components crack from excess clamping force; torque-to-yield (TTY) bolts must never be reused after being over-torqued. TORQUE WRENCH TYPES: CLICK-TYPE (most common) — preset the desired torque; wrench clicks and breaks over when target torque is reached; most reliable for consistent use; BEAM-TYPE — a pointer indicates torque on a scale as you apply force; simple, no preset required, accurate if read carefully; DIGITAL — shows exact torque on a display; some record peak torque; TORQUE ANGLE — measures both torque and rotation angle for TTY bolts; PROPER USE: Apply torque smoothly and steadily; a rapid jerk can overshoot; for critical fasteners, apply in stages (50%, 75%, 100% of final torque); retorque after initial use if required. IMPACT WRENCHES provide no torque control — they are for rapid removal/installation, not final torquing of precision fasteners. UNITS: ft-lbs (foot-pounds) and Nm (Newton-meters) are both common; 1 ft-lb = 1.356 Nm.

A box-end wrench fully encloses the fastener head, distributing force evenly around all six (or twelve) points. An open-end wrench contacts only two flat sides, concentrating force and allowing the wrench to slip and round off the fastener if excessive force is applied. Box-end wrenches are preferred for breaking loose tight fasteners because of this 360° grip advantage.

Technically, a BOLT is designed to be tightened by a nut on the opposite side — it clamps two parts together through holes. A SCREW is designed to thread directly into a material (wood, metal, plastic) without a separate nut. In practical shop use, these definitions blur — 'machine screw' often refers to what is technically a bolt when used with a nut. The key concept: bolt + nut = clamping joint; screw = threads into material directly.

A NAIL is driven straight in (usually with a HAMMER) and holds by FRICTION; a SCREW has THREADS, is turned in (with a screwdriver/drill), grips more SECURELY (the threads bite into the material), and can be easily removed. ASVAB Shop Information tests fasteners. Screws provide stronger, more reliable holding power and can be unscrewed; nails are faster to install but hold less securely and are harder to remove cleanly. Knowing the nail-vs-screw distinction (friction vs threads, holding strength, removability) is commonly tested.

A flat washer spreads the clamping force of a bolt or nut over a larger area, which distributes the load and protects the surface from damage and from the fastener digging in. A lock washer (split or toothed) adds tension or bite that helps keep the nut or bolt from vibrating loose. Washers are simple but important fasteners-system components. Choosing and placing washers correctly improves the strength and durability of a bolted joint. Understanding the role of washers — load distribution and, for lock washers, resisting loosening — is part of the fasteners topic.

A nail is a straight fastener driven in with a hammer; it goes in quickly and offers good resistance to shear (sideways) forces, making it common in framing. A screw has threads and is turned in with a screwdriver or drill; the threads grip the material and give much greater holding (pull-out) power and the ability to be removed and reused. Screws take longer to install but hold better in applications subject to pulling forces. Choosing nails for speed and shear strength versus screws for holding power is a practical fasteners concept on the Shop subtest.