Thread table — metric, BSP/G and NPT threads
This thread table covers the most commonly used thread standards in the stainless steel industry: metric ISO/DIN threads, BSP/G standard (DIN ISO 228), and NPT standard (ANSI B1.20.1) threads. The table includes the outer diameter, pitch, and recommended drill diameter.
? Thread reference table
Metric threads (ISO / DIN 13)
| Thread | Outer Ø (mm) | Pitch P (mm) | Drill (mm) |
|---|---|---|---|
| M3 | 3,0 | 0,50 | 2,50 |
| M4 | 4,0 | 0,70 | 3,30 |
| M5 | 5,0 | 0,80 | 4,20 |
| M6 | 6,0 | 1,00 | 5,00 |
| M8 | 8,0 | 1,25 | 6,75 |
| M10 | 10,0 | 1,50 | 8,50 |
| M12 | 12,0 | 1,75 | 10,25 |
| M14 | 14,0 | 2,00 | 12,00 |
| M16 | 16,0 | 2,00 | 14,00 |
| M18 | 18,0 | 2,50 | 15,50 |
| M20 | 20,0 | 2,50 | 17,50 |
| M22 | 22,0 | 2,50 | 19,50 |
| M24 | 24,0 | 3,00 | 21,00 |
| M27 | 27,0 | 3,00 | 24,00 |
| M30 | 30,0 | 3,50 | 26,50 |
| M36 | 36,0 | 4,00 | 32,00 |
| M42 | 42,0 | 4,50 | 37,50 |
| M48 | 48,0 | 5,00 | 43,00 |
BSP / G threads (DIN ISO 228)
| Thread | Outer Ø (mm) | Pitch (mm) | Row/col. |
|---|---|---|---|
| G 1/8" | 9,728 | 0,907 | 28 |
| G 1/4" | 13,157 | 1,337 | 19 |
| G 3/8" | 16,662 | 1,337 | 19 |
| G 1/2" | 20,955 | 1,814 | 14 |
| G 3/4" | 26,441 | 1,814 | 14 |
| G 1" | 33,249 | 2,309 | 11 |
| G 1 1/4" | 41,910 | 2,309 | 11 |
| G 1 1/2" | 47,803 | 2,309 | 11 |
| G 2" | 59,614 | 2,309 | 11 |
| G 2 1/2" | 75,184 | 2,309 | 11 |
| G 3" | 87,884 | 2,309 | 11 |
| G 4" | 113,030 | 2,309 | 11 |
NPT threads (ANSI B1.20.1)
| Thread | Outer Ø (mm) | Pitch (mm) | Row/col. |
|---|---|---|---|
| NPT 1/8" | 10,287 | 0,941 | 27 |
| NPT 1/4" | 13,716 | 1,411 | 18 |
| NPT 3/8" | 17,145 | 1,411 | 18 |
| NPT 1/2" | 21,336 | 1,814 | 14 |
| NPT 3/4" | 26,670 | 1,814 | 14 |
| NPT 1" | 33,401 | 2,209 | 11,5 |
| NPT 1 1/4" | 42,164 | 2,209 | 11,5 |
| NPT 1 1/2" | 48,260 | 2,209 | 11,5 |
| NPT 2" | 60,325 | 2,209 | 11,5 |
| NPT 3" | 88,900 | 2,209 | 11,5 |
| NPT 4" | 114,300 | 2,209 | 11,5 |
Thread standards — main differences
Metric threads (M)
Metric threads (ISO 68-1, DIN 13) — the most universal in Europe. Marked with the letter M + nominal diameter mm. E.g., M12 × 1.75 — 12 mm diameter thread with a 1.75 mm pitch.
BSP / G threads
British Standard Pipe (BSP) or G type threads according to DIN ISO 228 are used in piping systems, fittings, and valves. Cylindrical (G) and conical (R/BSPT) variants.
NPT threads
NPT (National Pipe Taper) — conical profile threads, common in the USA and Canada. Used for leak-proof connections without additional seals. Not compatible with BSP threads.
Frequently asked questions
How to distinguish between G and NPT threads?
G threads are cylindrical (parallel), NPT are conical (tapered). G pitches are measured in mm, NPT in threads per inch. The outer diameter also differs slightly.
What drill diameter is required for M10 thread?
Standard drill for M10 × 1.5 thread — 8.5 mm.
Does Karuselė supply threaded fittings?
Yes — the range of stainless steel fittings includes G and metric threads. If you have questions — The assortment includes G and metric threads. For inquiries — contact us.
Which thread is most commonly used in the food industry?
In the food industry, DIN 11851 milk threads or metric threads in AISI 316 stainless steel fittings are most commonly used, as they are easy to clean and disinfect.