Thread Identification Guide
Quickly identify your BSP, SMS and DIN threaded fittings using the dimension tables below.
BSP Standard
BSP / Gas (Inches)
BSP (or Gas) fittings : The standard for general plumbing, industry and hydraulics.
Thread form
Triangular (55° angle) — “V” profile providing mechanical locking and sealing.
Warning
The size in inches does not match the actual measurement (1″ ≈ 33.2 mm, not 25.4 mm).
| Inches | French size | ⌀ Outer Male | ⌀ Inner Female |
|---|---|---|---|
| 1/8″ | 5 × 10 | ~ 9.7 mm | ~ 8.5 mm |
| 1/4″ | 8 × 13 | ~ 13.1 mm | ~ 11.4 mm |
| 3/8″ | 12 × 17 | ~ 16.6 mm | ~ 14.9 mm |
| 1/2″ | 15 × 21 | ~ 20.9 mm | ~ 18.6 mm |
| 3/4″ | 20 × 27 | ~ 26.4 mm | ~ 24.1 mm |
| 1″ | 26 × 34 | ~ 33.2 mm | ~ 30.2 mm |
| 1″ 1/4 | 33 × 42 | ~ 41.9 mm | ~ 38.9 mm |
| 1″ 1/2 | 40 × 49 | ~ 47.8 mm | ~ 44.8 mm |
| 2″ | 50 × 60 | ~ 59.6 mm | ~ 56.6 mm |
SMS Standard
SMS (Food & Beverage)
SMS fittings (Swedish Metric Standard) : Widely used in the food and beverage industry. Recognisable by their round notched nut and a flat gasket with a rectangular cross-section. The nominal size corresponds to the outside diameter of the weld tube.
Thread form
Round (“Rd” profile) — prevents bacteria retention, easy to clean.
💡
Don’t confuse SMS and DIN! Although they look alike (round thread, notched nut), their thread diameters are different and not compatible.
| SMS size | ⌀ Outer Male | ⌀ Inner Female | ⌀ Bore | ⌀ Outer Tube |
|---|---|---|---|---|
| SMS 25 | ~ 40.0 mm | ~ 35.8 mm | 22.5 mm | 25 / 25.4 mm |
| SMS 38 | ~ 60.0 mm | ~ 55.8 mm | 35.5 mm | 38 / 38.1 mm |
| SMS 51 | ~ 70.0 mm | ~ 65.8 mm | 48.5 mm | 51 mm |
| SMS 63 | ~ 85.0 mm | ~ 80.8 mm | 60.5 mm | 63.5 mm |
| SMS 76 | ~ 98.0 mm | ~ 93.8 mm | 72.9 mm | 76.1 mm |
| SMS 104 | ~ 125.0 mm | ~ 118.6 mm | 100.0 mm | 104 mm |
DIN Standard
DIN 11851 (Food / Chemical)
DIN fittings (e.g. DIN 11851) : Found everywhere in the food, chemical and pharmaceutical industries. They look like SMS but often use a “D”-shaped O-ring with a lip. For an equivalent tube diameter, the DIN thread is always wider than the SMS.
Thread form
Round (“Rd” profile) — same hygiene reasons as SMS.
Nominal size
DN = European standard designation.
💡
Don’t confuse SMS and DIN! Despite their physical similarity, their thread diameters differ and they are not interchangeable.
| DN size | ⌀ Outer Male | ⌀ Inner Female | ⌀ Bore | ⌀ Outer Tube |
|---|---|---|---|---|
| DN 15 | ~ 34.0 mm | ~ 31.1 mm | 16 mm | 19 mm |
| DN 20 | ~ 44.0 mm | ~ 40.2 mm | 20 mm | 23 mm |
| DN 25 | ~ 52.0 mm | ~ 48.1 mm | 26 mm | 29 mm |
| DN 32 | ~ 58.0 mm | ~ 54.2 mm | 32 mm | 35 mm |
| DN 40 | ~ 65.0 mm | ~ 61.2 mm | 38 mm | 41 mm |
| DN 50 | ~ 78.0 mm | ~ 74.2 mm | 50 mm | 53 mm |
| DN 65 | ~ 95.0 mm | ~ 91.2 mm | 66 mm | 70 mm |
| DN 80 | ~ 110.0 mm | ~ 104.3 mm | 81 mm | 85 mm |