ISO 1222 Photography Tripod Screw Threads (1/4"-20 & 3/8"-16)
Direct Answer
ISO 1222 defines the standard mechanical screw threads used to mount photographic cameras, lighting accessories, and tripod heads. Standardizing on imperial UNC threads: 1/4"-20 UNC for camera baseplates and accessory cold shoes, and 3/8"-16 UNC for heavy tripod apex bases, fluid heads, and professional microphone boom poles.
Source: ISO 1222:2010 (Photography — Tripod connections) / ANSI/ASME B1.1
Specs
| Standard Camera Base Thread | 1/4"-20 UNC (1/4 inch diameter, 20 threads per inch, 60° Unified Coarse thread) |
| Standard Tripod Head Base Thread | 3/8"-16 UNC (3/8 inch diameter, 16 threads per inch) |
| Camera Female Socket Depth | Minimum 5.5 mm to 6.5 mm thread depth in camera base |
| Male Screw Thread Length | Standard 4.5 mm to 5.0 mm threaded protrusion (prevents bottoming out against internal sensor chassis) |
| Reducer Bushing Adapter | Brass/steel 3/8"-16 to 1/4"-20 slotted reducer bushing (converts 3/8" sockets to 1/4" studs) |
| Domain Ubiquity | Universal across all DSLR/mirrorless camera bases, tripod quick-release plates, gimbal studs, monitor arms |
Why Cameras Still Use Imperial Threads
Even in 100% metric countries (Japan, Germany), all cameras use 1/4"-20 UNC and 3/8"-16 UNC threads standardized by the British Royal Photographic Society in 1891 and formalized globally as ISO 1222. An M6 metric screw will thread into a 1/4"-20 socket for half a turn before seizing and stripping the brass camera socket.