#8-32 UNC Thread
Direct Answer
8-32 UNC is a numbered Unified Coarse machine screw thread with a major diameter of 0.1640 inches (4.166 mm) and 32 threads per inch (TPI). Requiring a #29 (0.1360 inch) tap drill, it is the standard fastener for North American electrical ceiling junction boxes, light fixtures, and kitchen cabinet hardware knobs.
Source: ANSI/ASME B1.1 / NEMA OS 1
Specs
| Nominal Major Diameter | 0.1640 in (4.166 mm) |
| Threads Per Inch (TPI) | 32 TPI (Coarse pitch: 0.794 mm) |
| Fine Pitch Equivalent | #8-36 UNF (0.706 mm pitch) |
| Tap Drill Size | #29 drill bit (0.1360 in / 3.45 mm) |
| Minor Diameter (Internal) | 0.1302 in (3.307 mm) |
| Tensile Stress Area | 0.0140 in² (9.03 mm²) |
| Common Drive Size | PH2 / Slotted / Square #2 |
Electrical Ceiling Boxes and Fixture Mounts
While standard wall outlets use #6-32 screws, heavy-duty 4-inch round/octagonal electrical ceiling boxes (used for hanging ceiling light fixtures, smoke detectors, and ceiling fans) use #8-32 screws to provide higher shear load support.
Cabinet Knobs and Drawer Pulls
In North American kitchen and bathroom cabinetry, standard cabinet knobs and decorative drawer pulls are mounted with 1-inch or 1.5-inch #8-32 truss-head machine screws.