Match driver type to screw recess: SLOTTED (flat-head) has straight slot; one of the oldest types; can slip out (cam-out) easily under torque; flat-blade screwdriver fits; sizes by blade width (1/8 inch, 3/16 inch, 1/4 inch common). PHILLIPS has cross-shaped (+) recess; designed to cam-out at high torque (originally as a safety/torque-limiting feature); Phillips screwdriver fits; sizes #00, #0, #1, #2 (most common for general work), #3 (large); #2 fits most household and electronic screws. POZIDRIV is similar to Phillips but with additional radial lines/ribs; less prone to cam-out; common in European applications and electronics; can damage Phillips bits if forced. ALLEN or HEX has hexagonal recess; uses hex key (Allen wrench) L-shaped tool; very common in furniture (IKEA), bicycles, machinery; metric and SAE sizes. TORX (STAR) has six-pointed star recess; designed for high torque without cam-out; common in automotive, electronics, machinery; sizes T1 (very small) to T100; security torx has a center pin to prevent standard torx bits from working. SQUARE or ROBERTSON has square recess; Canadian invention; very good engagement; common in cabinetry, decking; sizes R0 (yellow), R1 (green), R2 (red), R3 (black). SPLINE or 12-POINT is for automotive and aerospace. TRI-WING, TORQ-SET, BRISTOL are security screws used in electronics and aerospace; require specialized drivers.
Proper use: match the size; press down firmly while turning (downward force) since many screws back out easily because of insufficient pressure; use straight (angled drivers cam out easily); longer handle equals more torque; don't hammer on a screwdriver unless it's a special impact/striking screwdriver.
Stripped screws: when recess is damaged, remedies include rubber band between driver and recess; tapping driver to engage; screw extractor (drill into screw head, then back out with reverse-thread extractor); left-handed drill bits (can grab and unscrew while drilling); pliers or Vise-Grips on protruding head. RIGHTY-TIGHTY, LEFTY-LOOSEY: for most screws clockwise tightens and counterclockwise loosens (viewed from driver end). Exceptions: left-handed threads are used on some applications like left-side wheel lug nuts on older cars, opposite-handed pedal threads on bicycles, gas tank caps, propane fittings, to prevent loosening from rotation.