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.