#8 Screw Size and Thread Specifications
#8 is a common numbered screw size. #8-32 (32 TPI) is widely used in electronics, machinery, and hardware. Diameter is approximately 0.164 in (4.2 mm), close to metric M4. Spanish reference: metric & UNC size pages (ES). For tap drill size, thread types, and thread identifier workflows, pair this page with tools as you verify threads.
Specifications
| Specification | Value |
|---|---|
| Designation | #8-32 (common) |
| Diameter | 0.164 in (4.2 mm) |
| Threads per inch (TPI) | 32 |
| Tap drill size | #29 |
| Closest metric equivalent | M4 |
Head types
| Screw size | Common head types |
|---|---|
| #8 | Pan head, flat head, round head (Phillips, slot, hex) |
Common uses
#8 screws are used in electronics, machinery, furniture, and general hardware. #8-32 is a standard thread for machine screws and is widely available. Cross-check loads with the bolt size chart and screw size conversion when you mix metric and inch bins.
Related tools
Related charts
#8 vs #10 screw size
Shank diameter and TPI change load capacity, wrench sizes, and required tap drill size before tapping. Compare tables on this page with the
Compare tables on this page with the #10 spec page.
Use the bolt size chart for full context.
Metric vs UNC thread size
Metric threads list diameter in millimeters and pitch in millimeters per thread; UNC lists nominal inch diameter and threads per inch. They are not interchangeable—taps, dies, and gauges differ.
Read metric vs unc thread context when series labels are unclear.
Use screw size conversion when you must match stocked parts.
How to choose the right bolt size
Choosing the correct bolt size depends on load, material, and thread type. Larger diameters increase strength, while thread pitch affects holding force.
Use the bolt size chart to compare shank and hex dimensions before you standardize hardware.
Use tap drill size guidance when you plan tapped holes.
Use the thread identifier when stamped sizes are missing.
FAQ
What is #8 screw size?
#8 is a numbered (wire gauge) screw size. #8-32 means a #8 diameter with 32 threads per inch. Diameter is approximately 0.164 in (4.2 mm).
What drill size for #8-32 tap?
Use a #29 drill for #8-32 tapping.
What metric screw is closest to #8?
M4 is the closest metric equivalent to #8. See M4 bolt size for full specs.