#4-40 UNC Thread
Direct Answer
4-40 UNC is a numbered Unified Coarse machine screw thread with a major diameter of 0.1120 inches (2.845 mm) and 40 threads per inch (TPI). Requiring a #43 (0.0890 inch) tap drill, it is the worldwide computing standard for D-subminiature connector jackscrews (VGA, DVI, RS-232 serial ports).
Source: ANSI/ASME B1.1 / EIA RS-232 / VESA Display Standards
Specs
| Nominal Major Diameter | 0.1120 in (2.845 mm) |
| Threads Per Inch (TPI) | 40 TPI (Coarse pitch: 0.635 mm) |
| Fine Pitch Equivalent | #4-48 UNF (0.529 mm pitch) |
| Tap Drill Size | #43 drill bit (0.0890 in / 2.26 mm) |
| Minor Diameter (Internal) | 0.0849 in (2.156 mm) |
| Tensile Stress Area | 0.00604 in² (3.90 mm²) |
| Common Computing Role | D-sub / VGA / DVI thumbscrew standoffs |
The Video Cable Standoff Standard
On virtually all computer monitors, graphics cards, and legacy motherboard I/O shields, the hex standoff nuts flanking VGA (DE-15), DVI, and RS-232 serial ports (DB-9, DB-25) are threaded with #4-40 UNC internal threads. The knurled thumbscrews on mating cables use matching #4-40 male threads.
Differences with M3
Because #4-40 (2.84 mm major diameter, 0.635 mm pitch) is very close in diameter to M3 (3.00 mm major diameter, 0.50 mm pitch), users frequently attempt to force M3 screws into #4-40 connector standoffs, resulting in thread binding after 1–2 turns.