Hand and Power Tools, Fasteners, and Rigging
Tools
Inspect before each use. A grinding wheel's rated maximum rpm must equal or exceed the tool's spindle rpm, the guard stays in place, and the tool rest sits within about 1/8 in. of the wheel. Dress or discard chisels with mushroomed heads. Never use a cheater bar on a torque wrench, and never use a wrench as a hammer.
Fasteners
Know the markings: inch-grade bolts show radial lines (Grade 5 has three, Grade 8 has six); metric bolts show a property class (8.8, 10.9, 12.9). Coarse threads are stronger in soft materials and resist galling; fine threads give more clamping force per turn and resist vibration. Torque produces clamping force, and lubrication changes the torque-to-tension relationship. Left-hand threads appear on some shafts and on one end of turnbuckles.
Rigging
Every sling has a working load limit that applies to a vertical pull. When legs spread, capacity drops by the multiplier 1/sin θ, where θ is the angle from horizontal. At 60° each leg carries 0.577 of the load; at 45°, 0.707; at 30°, a full 1.0. Never side-load a hook, never let a sling chafe on a sharp edge, always know the center of gravity, and use taglines for control.
Worked example
A 4,000 lb load hangs from a two-leg bridle at 45° from horizontal. Load per leg = 4,000 ÷ (2 × sin 45°) = 4,000 ÷ 1.414 ≈ 2,828 lb per leg. Two 3,000 lb slings are acceptable; two 2,000 lb slings are not.