Fastener Torque Reference Card

Why this matters

Under-torqued fasteners loosen + cause failure (HVAC equipment vibration loosens screws + customer's coil falls; electrical lug under-torqued = arcing + fire; plumbing flange not torqued = leak). Over-torqued = stripped threads + cracked components + customer's fixture replaced because tech kept turning. The handful of pieces of data techs need is small + worth memorizing. This is the field card.

Hex bolt + cap screw torque (dry, no lube)

Grade 5 / Class 8.8 - most common construction:

Grade 8 / Class 10.9 - premium structural (multiply by ~1.4; Grade 8 proof load is 120 ksi against Grade 5's 85 ksi):

Lubricated torque: reduce dry value by 20 - 25%.

Metric hex bolt torque

Class 8.8 (most common):

Class 10.9 - multiply by 1.4. Class 12.9 - multiply by 1.6.

Electrical lug torque (NEC + UL listing)

Lug torque varies by manufacturer. Common values for copper conductors in aluminum / copper lugs:

NEVER guess electrical lug torque - manufacturer's listed value on equipment OR per UL listing. Wrong torque = arc-fault risk.

Wood screws / drywall screws

Driven to flush + slight set, not torque-spec'd:

• Driver clutch setting: light to medium for cabinetry; medium to heavy for framing
• Pre-drill for hardwoods (oak, maple, walnut)
• Drywall screws: surface flush, paper not torn, slight dimple

Plumbing fitting torque

Threaded fittings (NPT) are hand-tighten + 1 - 3 turns past tight with wrench. NOT torque-spec'd. Use thread sealant (yellow PTFE for gas, white PTFE for water). Stop turning before splitting brass fitting.

Cast iron fittings: 4 - 6 turns past hand-tight; use proper-size wrench (Ridgid pipe wrench for cast iron).

CSST gas fittings: per manufacturer spec (Gastite, Tracpipe). Typically 8 - 50 ft-lb depending on size.

HVAC flare connections

Refrigerant line flare nuts:

Critical: flare must be properly formed (correct angle, no scratches). Use refrigerant oil on threads. Over-torque cracks flare; under-torque leaks.

Anchor bolt torque (concrete)

Depends on anchor type + diameter. Common:

• 1/4" wedge anchor: 8 - 15 ft-lb
• 3/8" wedge anchor: 25 - 40 ft-lb
• 1/2" wedge anchor: 60 - 90 ft-lb
• 5/8" wedge anchor: 105 - 175 ft-lb

Adhesive anchors: per manufacturer spec; usually 80 - 120% of mechanical anchor torque.

Roofing fasteners

Most roofing fasteners not torque-spec'd:

• Asphalt shingle nails: full driven to surface, not over-driven (causes tear)
• Wood roof: countersink slightly
• Metal roof: per manufacturer; sealed screws need gasket compressed (not over-compressed)
• Hurricane straps: per engineer's spec

Garage door bolts

Cable drum and spring fixtures are the critical ones, and they are NOT a ft-lb spec. Both drums and winding cones clamp with cup-point socket set screws, usually 1/4-20 or 5/16-18. Look at the Grade 5 table above: a 1/4-20 tops out around 8 ft-lb and a 5/16-18 around 17. Anything in the tens of ft-lb shears the screw or galls the shaft, and any chart telling you 50+ ft-lb on a set screw is wrong.

• Cable drum set screws: run the screw down until it contacts the shaft, then the additional fraction of a turn the drum manufacturer specifies. The point is to bite a flat into the shaft, not to stretch the screw.
• Torsion spring winding cone set screws: same method, per the spring hardware manufacturer's printed instruction. This is the one that kills people if it slips, so use the sheet that came with the hardware and no other number.
• Hinge and roller bracket lags/screws: snug to the door skin without crushing it. Per manufacturer.

Do not substitute a generic torque chart for garage door spring hardware - a slipped cone under load releases the full spring wind at once.

Stripped fastener removal

When fastener strips:

• Center punch + drill out (for unspecified bolts)
• Easy-out + extractor (rare success)
• Cut head + slot + slot screwdriver (for heads)
• Welding nut to bolt + back out (last resort)
• Replace with next-size-up fastener

Tightening + torquing sequence

For multi-bolt assemblies (cylinder heads, flanges, etc.):

• Star pattern: always jump to the bolt across from the last one. On 8 bolts numbered around the circle that is 1-5-3-7-2-6-4-8, not 1-2-3-4 and not 1-3-5-7 (adjacent-ish bolts pull the joint crooked)
• Snug + then incremental torquing (50% → 75% → 100%)
• Don't fully torque any single bolt until others are at least 50%
• Check + re-torque after thermal cycling (HVAC, automotive)

Torque tool calibration

Click + dial torque wrenches drift over time:

• Calibrate annually (most calibration labs)
• Mark "calibrated" on tool
• Industrial: more frequent calibration
• Hand-tight + 1-turn estimation OK for non-critical

Common over-torque damage

• Stripped wood/drywall fasteners (replace + relocate)
• Cracked brass plumbing fittings (replace)
• Crushed cable insulation (rewire)
• Stripped electrical lugs (replace breaker OR re-strip wire)
• Broken HVAC flare (rebuild)

Common under-torque damage

• Loosened fastener over time (vibration)
• Leaking plumbing (drips → mold → damage)
• Loose electrical connections (arcing, fire)
• Failed HVAC refrigerant connections (leak + system failure)

References

• ANSI/ASME B18 (fastener standards)
• NEC 110.14 (electrical termination torque)
• AGCC + manufacturer specs (HVAC flare torque)
• Bolt Science (industry training)
• Manuall internal: Conductor Ampacity Reference, Common Fittings Reference