Socket Square Drive Sizes
Tool Drives & Bit Shanks · 7 specs
Direct Answer
Square socket drives are standardized under ISO 1174-1 and ASME B107 into five standardized fractional inch drive square tiers: 1/4-inch, 3/8-inch, 1/2-inch, 3/4-inch, and 1-inch, each defining maximum safe working torque limits, retaining ball detent locations, and pin-hole locks.
Source: ISO 1174-1:2011 Assembly tools for screws and nuts — Driving squares / ASME B107.4M · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ISO 1174-1 (Hand Tools) / ISO 1174-2 (Power / Impact Tools) / ASME B107.4M |
| 1/4-Inch Drive (6.3 mm) | Drive Square: 6.35 mm | Torque Limit: ~30 to 45 N·m (22–33 lbf·ft) | Typical Socket Range: 4 mm to 14 mm (5/32" to 9/16") |
| 3/8-Inch Drive (10.0 mm) | Drive Square: 9.53 mm | Torque Limit: ~150 to 200 N·m (110–148 lbf·ft) | Typical Socket Range: 8 mm to 22 mm (5/16" to 7/8") |
| 1/2-Inch Drive (12.5 mm) | Drive Square: 12.70 mm | Torque Limit: ~500 to 650 N·m (370–480 lbf·ft) | Typical Socket Range: 10 mm to 36 mm (3/8" to 1-1/2") |
| 3/4-Inch Drive (20.0 mm) | Drive Square: 19.05 mm | Torque Limit: ~1,400 to 1,800 N·m (1,030–1,330 lbf·ft) | Semi-truck, tractor, structural bolting |
| 1-Inch Drive (25.0 mm) | Drive Square: 25.40 mm | Torque Limit: ~2,800 to 3,500 N·m (2,060–2,580 lbf·ft) | Heavy earthmoving machinery, mining, industrial |
| Retaining Mechanisms | Spring-loaded steel ball detent (Chrome hand sockets) vs Pin-hole & rubber O-ring (Impact power sockets) |
Standard Socket Drive Size & Working Torque Matrix
| Drive Size (Nominal) | Exact Square Dimension | Metric ISO Code | Maximum Safe Torque Rating | Primary Mechanical Application | Typical Fastener Socket Range |
|---|---|---|---|---|---|
| 1/4-Inch (1/4") | 6.35 mm (0.250") | ISO 6.3 | 45 N·m (33 lbf·ft) | Electronics, dashboard trim, bicycles, small engines | 4.0 mm to 14.0 mm (5/32"–9/16") |
| 3/8-Inch (3/8") | 9.53 mm (0.375") | ISO 10 | 200 N·m (148 lbf·ft) | Automotive engine bay, brake calipers, spark plugs | 8.0 mm to 22.0 mm (5/16"–7/8") |
| 1/2-Inch (1/2") | 12.70 mm (0.500") | ISO 12.5 | 650 N·m (480 lbf·ft) | Wheel lug nuts, suspension control arms, cylinder heads | 10.0 mm to 36.0 mm (3/8"–1-1/2") |
| 3/4-Inch (3/4") | 19.05 mm (0.750") | ISO 20 | 1,800 N·m (1,330 lbf·ft) | Semi-truck wheel hubs, heavy tractors, cranes | 19.0 mm to 60.0 mm (3/4"–2-3/8") |
| 1-Inch (1") | 25.40 mm (1.000") | ISO 25 | 3,500 N·m (2,580 lbf·ft) | Mining excavators, railway tracks, wind turbines | 24.0 mm to 100.0+ mm (1"–4") |
Chrome Vanadium vs Chrome Molybdenum (Impact Sockets)
- Chrome Vanadium (Cr-V) Hand Sockets: Hardened steel with a mirror chrome finish. Highly rigid to prevent torsional flexing by hand, but brittle under high-frequency impact hammer blows (risking catastrophic shattering).
- Chrome Molybdenum (Cr-Mo) Impact Sockets: Treated with ductile black oxide. Slightly softer and more ductile to absorb repetitive pneumatic and cordless impact wrench shocks without cracking.