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:
| Size | Torque (ft-lb) |
|---|---|
| 1/4-20 | 7 - 10 |
| 5/16-18 | 14 - 18 |
| 3/8-16 | 25 - 33 |
| 7/16-14 | 40 - 53 |
| 1/2-13 | 60 - 80 |
| 9/16-12 | 88 - 115 |
| 5/8-11 | 125 - 165 |
| 3/4-10 | 220 - 290 |
| 7/8-9 | 350 - 470 |
| 1-8 | 525 - 700 |
Grade 8 / Class 10.9 - premium structural (multiply by ~1.3):
| Size | Torque (ft-lb) |
|---|---|
| 1/4-20 | 10 - 14 |
| 3/8-16 | 35 - 45 |
| 1/2-13 | 85 - 110 |
| 5/8-11 | 170 - 220 |
| 3/4-10 | 300 - 400 |
| 1-8 | 700 - 900 |
Lubricated torque: reduce dry value by 20 - 25%.
Metric hex bolt torque
Class 8.8 (most common):
| Size | Torque (Nm) | Torque (ft-lb) |
|---|---|---|
| M6 | 9 - 12 | 7 - 9 |
| M8 | 22 - 30 | 16 - 22 |
| M10 | 45 - 60 | 33 - 44 |
| M12 | 78 - 105 | 58 - 78 |
| M14 | 125 - 165 | 92 - 122 |
| M16 | 195 - 260 | 144 - 192 |
| M18 | 270 - 360 | 200 - 265 |
| M20 | 390 - 525 | 288 - 388 |
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:
| Wire size (AWG) | Torque (in-lb) |
|---|---|
| 14 | 14 - 18 |
| 12 | 14 - 18 |
| 10 | 25 - 35 |
| 8 | 40 |
| 6 | 45 - 55 |
| 4 | 60 |
| 2 | 70 - 90 |
| 1/0 | 120 |
| 2/0 | 150 |
| 4/0 | 180 |
| 250 kcmil | 200 - 250 |
| 350 kcmil | 250 - 325 |
| 500 kcmil | 325 - 425 |
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:
| Tube OD | Torque (ft-lb) |
|---|---|
| 1/4" | 11 - 15 |
| 3/8" | 23 - 30 |
| 1/2" | 33 - 42 |
| 5/8" | 41 - 52 |
| 3/4" | 60 - 75 |
| 7/8" | 70 - 90 |
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 + spring fixtures critical:
- Cable drum hub set screws: 50 - 70 ft-lb (engineering grade)
- Torsion spring cone set screws: 65 - 85 ft-lb (engineering grade)
- Hinge bolts: 15 - 25 ft-lb typical
- Roller brackets: per manufacturer
Always use torque wrench on garage door spring components - under-torque = release + injury.
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.):
- Cross pattern (1-3-5-7 then 2-4-6-8 for 8 bolts)
- 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)
The single highest-leverage torque habit is the TORQUE WRENCH USAGE in critical applications. Garage door spring tensioner: torque wrench. Refrigerant flare: torque wrench. Electrical lug above 50A: torque wrench. Customer doesn't see the difference, but the longevity + safety + warranty-claim outcome differs dramatically. Most techs guess; the pros use torque wrenches for critical connections + own the warranty calls that result from wrong torque on those connections.
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