What size is a 0000 screw

A #0000 (or 4-0) screw has a major diameter of approximately 0.034 inches (about 0.86 mm), making it one of the smallest standard precision screws available. These micro-fasteners are used exclusively in watches, precision instruments, eyeglasses, electronics miniaturization, and other applications where conventional fasteners would be impossibly large. The screw size numbering below #0 continues into negative territory: #00 (double-ought), #000 (triple-ought), and #0000 (quadruple-ought), each progressively smaller.

Handling and installing 0000 screws requires specialized tools including precision screwdrivers (typically 0.5-0.8 mm blade width), magnification for visibility, and often steady-hand techniques used by watchmakers and precision instrument technicians. Thread engagement is critical at this scale—overtightening with even minimal force strips threads in softer materials, while under-tightening fails to secure components. These screws typically feature fine thread pitches (often 160 threads per inch or finer) to maximize thread engagement in the minimal available material depth. Thread forms at this scale may be cut, rolled, or formed depending on material and application. For anyone outside specialized precision industries, encountering 0000 screws is rare, and attempting DIY repair of devices using such fasteners without proper tools, magnification, and technique often results in damaged screw heads, stripped threads, or lost components due to their minuscule size.