Tools and Equipment
Fasteners and torque
Know the head markings: SAE Grade 5 shows three radial lines, Grade 8 shows six; metric property classes 8.8, 10.9, and 12.9 are stamped numerically. Torque is only a proxy for bolt preload, approximated by T = K·D·F, with K near 0.20 for dry, as-received steel threads. Lubricated threads cut friction, so the same torque produces higher preload and can over-stretch the bolt. Torque-to-yield and turn-of-nut fasteners are single-use. Follow the specified pattern and staged increments.
Hand and power tools
Inspect before use. No cheater bars on wrenches, no chisels with mushroomed heads, no screwdrivers used as pry bars, guards in place on grinders, and wheel RPM rating matched to the tool. Hydraulic torque wrenches and multipliers need their reaction arms backed against a solid, non-damaging surface. Pullers need legs fully engaged and the screw centered.
Measuring and special tools
Torque wrenches are calibrated on a schedule and after any drop; store adjustable types at the lowest setting and never use a click type to break a fastener loose. Micrometers, calipers, feeler gauges, and dial indicators each have a correct application - a caliper is not a bore gauge. Cutting tools: tap drill size, thread pitch, and correct lubricant matter more than speed.
Traps
Assuming a longer handle or an extension does not change torque; assuming dry and lubricated torque are interchangeable; using an impact wrench on a torque wrench; mixing inch and metric hardware; treating a Grade 2 bolt as a Grade 5 substitute.
Rule of thumb
Torque scatter can reach ±25%. When the specification gives preload, stretch, or turn-of-nut, use that method instead of a torque value.