Global Araç
Screw Size Converter
Ölçü
#8
Metrik
M4
Çap
0.164"
Diş adımı (TPI)
Kaba: 32 TPI · İnce: 36 TPI
Başlık türleri
flat, pan, round, truss, button
Yaygın uzunluklar
Metrik dönüşüm nominaldir — M4 teknik olarak 0.157" ancak #8'e en yakın ticari eşdeğerdir. Yapısal kullanım için tam bağlantı standardını eşleştirin (inç için ANSI B18.6.3, metrik için ISO 1478).
Screw sizing has three parallel naming systems that all describe the same physical part — and switching between them is a daily headache for anyone working across regional hardware standards. The US uses gauge numbers (#0, #2, #4, #6, #8, #10, #12 — strange legacy of the Wire Gauge Standard from the 1840s) for screws under 1/4-inch and fractional inches above (1/4", 5/16", 3/8"). Europe, Japan, and most of the world use metric (M2, M3, M4, M5, M6, M8, M10) where the number is the major diameter in millimeters. UK has historic Whitworth and BSF systems, mostly obsolete except in restoration work. A #8 wood screw, an M4 machine screw, and a 0.164-inch diameter rod are all roughly the same thickness — but try finding that conversion in your head while standing in a hardware aisle.
The converter takes any one of those three naming inputs and shows the other two, alongside the relevant thread pitches (UNC coarse vs UNF fine for imperial; standard metric pitch in mm), common available lengths for that size, head-type compatibility (Phillips, flat, Pozidriv, Torx, hex, square), and the rough strength rating. Useful for: matching replacement screws when the original packaging is gone, ordering metric hardware for an imperial project (or vice versa), figuring out which pilot-drill-bit size to pre-drill, and double-checking before you order 100 of something that turns out to be the wrong standard.
Reference points: #6 ≈ M3.5 ≈ 0.138" (small wood screws, drywall screws). #8 ≈ M4 ≈ 0.164" (the most common all-purpose size for cabinetry, framing, and assembly). #10 ≈ M5 ≈ 0.190" (heavier wood and machine screws). 1/4" ≈ M6 ≈ 0.250" (the boundary between “screw” and “bolt” in many catalogs). Above that, fractional and metric standards diverge meaningfully and mixing them causes problems — never try to force an M8 bolt into a 5/16" threaded hole; the pitches don’t match and you’ll strip both.
Nasıl Kullanılır
- Enter your known size — gauge number (#8), metric (M4), or fractional inch (5/32").
- Read the equivalents in the other two naming systems.
- Check the listed thread pitches (UNC/UNF for imperial, standard metric pitch).
- Cross-reference common lengths and head types available for that size.
- Use the pilot-drill-bit recommendation for pre-drilling wood or soft materials.
Ne Zaman Kullanılır
- Replacing a lost screw and need to identify size from a sample.
- Ordering hardware in metric for a project that originally used imperial (or vice versa).
- Sourcing screws from international vendors (AliExpress, McMaster-Carr) where naming may differ.
- Pre-drilling pilot holes — the right bit size depends on screw size and material.
Ne Zaman Kullanılmaz
- Precision threaded fasteners for engineering applications — use the actual standard (ANSI B18, ISO 261) not approximations.
- Mating different-standard threads — even when sizes nearly match, thread pitch differs and forcing fasteners damages threads.
- Specialty fasteners (security screws, captive screws, weather-rated marine fasteners) where the head/material/coating matters more than nominal size.
- Whitworth/BSF restoration — those use a different thread angle (55° vs UN’s 60°) and aren’t cross-compatible with modern fasteners.
Yaygın Kullanım Senaryoları
- Onboarding a colleague who needs the same calculation/conversion
- Verifying a number or output before passing it on
- Quick conversion during a typical workday
- Pre-decision sanity-check on inputs and outputs
Sık Sorulan Sorular
Are #8 and M4 actually interchangeable?
Approximately the same diameter, but pitch differs. A #8-32 (UNC coarse) has 32 threads per inch; M4 standard pitch is 0.7mm. They will NOT thread into each other’s holes. Use the conversion for size matching only — for the actual hole/thread, stick to one standard end-to-end.
What's the difference between UNC and UNF threads?
Both are imperial thread standards. UNC (Unified Coarse) has fewer threads per inch — fast to drive, more forgiving in soft materials, used for general construction (1/4-20, 5/16-18, 3/8-16). UNF (Unified Fine) has more threads per inch — better holding power in metal, preferred for engine and aerospace applications (1/4-28, 5/16-24, 3/8-24). Most consumer hardware is UNC.
What pilot-drill size should I use?
Rule of thumb: pilot bit ~70% of screw shank diameter for hardwood, 50-60% for softwood, 90% for metal (matched-size for tap-drill). The tool lists recommended pilot sizes for each screw size in both inch fractional and metric. Better to drill slightly smaller and ream larger if needed than to oversize and lose holding power.
What does “gauge” actually measure?
Wire gauge is a legacy system where higher numbers mean thinner wire/screw. #0 is the smallest common gauge (~0.060" diameter), and gauge increases up to #14 or so. The relationship to actual diameter follows a formula, not a clean rule. Once you cross 1/4-inch, US screw sizing switches from gauge to fractional inch.
How do I read “M5x20” on a metric screw?
M = metric, 5 = 5mm major diameter, x20 = 20mm length. The standard pitch is implied (0.8mm for M5). For non-standard pitches (fine pitch), it would be written like M5x0.5x20. Length is typically measured under the head for flat/countersunk screws and under the head excluding the shoulder for socket-head and pan-head screws.
Are head types interchangeable across standards?
Mostly yes for diameter. A Phillips #2 driver fits both #8 imperial and M4 metric Phillips heads. Torx (T15, T20, T25) is increasingly used in both standards. The exception: some metric screws use Pozidriv (similar to Phillips but slightly different — Pozidriv has 4 small extra ribs at 45°). Using a Phillips driver on Pozidriv (or vice versa) cams out faster.