Stainless steel lock nut (backnut) 316, BSP threaded
Shipping and Delivery
Shipping and Delivery
| Product Type | Delivery Method | Preparation Time | Transport Time | Delivery Time |
|---|---|---|---|---|
| All Parts | Pickup Point | 0 to 3 days | 3 to 6 days | 3 to 9 days |
| All Parts | Home Delivery | 0 to 3 days | 3 to 5 days | 3 to 8 days |
| Tubes > 90cm | Home Delivery | 0 to 3 days | 3 to 5 days | 3 to 8 days |
| Tubes < 200cm | Home Delivery | 0 to 3 days | 3 to 5 days | 3 to 8 days |
| Tubes > 200cm | Home Delivery | 0 to 6 days | 6 to 10 days | 6 to 16 days |
| Assembled Products | Home Delivery & Pickup Point | 0 to 5 days | (see methods) | 3 to 11 days |
* Tubes longer than 90cm cannot be delivered to a pickup point
For orders of more than 50 units of the same item or more than 100 kg, restocking may exceptionally extend the delivery time by up to 10 working days.
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Stainless steel lock nut (backnut) 316, BSP threaded
Stainless steel lock nut (backnut) 316, tapped BSP (Rp to ISO 7-1), from 1/4" to 4" (DN8 to DN100). Screwed onto an R male thread, it locks an assembly or a fitting passing through a wall, but does not seal on its own. PN 20 up to 40 °C, drinking water compliant, for all fluids compatible with stainless steel.
Description of the stainless steel BSP lock nut
This stainless steel lock nut is a nut with flats, tapped right through. It bears against a component or a wall to lock the assembly in position. It is investment cast (lost wax) in CF8M (AISI 316) stainless steel, and designed, manufactured and inspected to ISO 4144.
It comes in 11 sizes, from 1/4" (French size 8x13) to 4" (102x114). Its thickness ranges from 6 mm at 1/4" to 22 mm at 4", and its dimension across flats from 21 to 134 mm. Dimensions and weights for each size are given below.
Stainless steel lock nut: technical specifications
| Material | CF8M (AISI 316) stainless steel |
| Manufacture | Investment casting (lost wax) |
| Standard | Designed, manufactured and inspected to ISO 4144 |
| Function | Locks an assembly or a fitting passing through a wall. Does not seal on its own |
| Shape | Nut with flats, tapped right through |
| Thread | Rp tapped (parallel) to ISO 7-1 (BSP, R series). Mates with an R male thread (taper). Not compatible with NPT |
| Connection | Female |
| Nominal pressure | PN 20: 20 bar from −20 to 40 °C, lower above that |
| Temperature | −20/+220 °C, permissible pressure reduced above 40 °C |
| Fluids | All fluids compatible with stainless steel |
| Sizes | 11 sizes, from 1/4" to 4" |
| Compliance | 4MS; drinking water: French order of 25 June 2020 |
Pressure and temperature
PN 20 applies from −20 to 40 °C. Above that, the permissible pressure falls. Values marked ≈ are read from the pressure/temperature curve in the technical data sheet.
| Temperature (°C) | Max. pressure (bar) |
|---|---|
| −20 → 40 | 20 |
| 100 | ≈ 16.5 |
| 150 | ≈ 15 |
| 220 | ≈ 13.5 |
Certification and compliance
According to the technical data sheet for the series:
- 4MS: compliant with the 4MS requirements, the harmonized European rules for materials and products in contact with drinking water.
- Drinking water: compliant with the French order (arrêté) of 25 June 2020 on metallic materials and products in contact with water intended for human consumption.
Uses and installation advice
This lock nut is used on drinking water systems and on circuits carrying fluids compatible with 316 stainless steel, to lock a threaded assembly or hold a component passing through a wall. Check fluid compatibility, and the permissible pressure of each component in the assembly at the working temperature.
- Sealing: the lock nut does not seal on its own. Sealing is dealt with separately, for example on the threads of an Rp/R joint, using PTFE or jointing compound suited to the fluid and the working temperature.
- Position on the thread: as an R male thread is tapered, the lock nut does not run down the full length of the thread. Check its position with a dry fit, as well as the thread length available.
- Galling: with stainless steel on stainless steel, the thread can gall. Screw in gradually, without forcing.
- Tightening: tighten with an open-ended or adjustable spanner on the flats, not with pipe grips or pliers, which mark stainless steel. Hold the male component while locking: a spanner on its flats, or a strap wrench on pipe.
- Dissimilar metals: on a water system, stainless steel forms a galvanic couple with galvanized steel or cast iron. Allow for this when choosing the connected components.
Technical drawing
Dimensions (mm)
A is the thickness of the lock nut and B its dimension across flats. Dimensions in millimetres, PN in bar, weight in kilograms.
| Rp size | French size | A | B | PN (bar) | Weight (kg) |
|---|---|---|---|---|---|
| 1/4" | 8x13 | 6 | 21 | 20 | 0.011 |
| 3/8" | 12x17 | 7 | 26 | 20 | 0.019 |
| 1/2" | 15x21 | 8 | 31 | 20 | 0.030 |
| 3/4" | 20x27 | 9 | 35 | 20 | 0.038 |
| 1" | 26x34 | 10 | 45 | 20 | 0.068 |
| 1"1/4 | 33x42 | 11 | 53.5 | 20 | 0.098 |
| 1"1/2 | 40x49 | 12 | 59 | 20 | 0.111 |
| 2" | 50x60 | 13 | 74 | 20 | 0.197 |
| 2"1/2 | 66x76 | 16 | 93.5 | 20 | 0.392 |
| 3" | 80x90 | 19 | 104.5 | 20 | 0.497 |
| 4" | 102x114 | 22 | 134 | 20 | 0.920 |
Size conversion
Conversion between the French size designation, inches, DN and the outside diameter stated in the designation (a rounded value, not a pipe dimension).
| French size | 8x13 | 12x17 | 15x21 | 20x27 | 26x34 | 33x42 | 40x49 | 50x60 | 66x76 | 80x90 | 102x114 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Inches | 1/4" | 3/8" | 1/2" | 3/4" | 1" | 1"1/4 | 1"1/2 | 2" | 2"1/2 | 3" | 4" |
| DN | DN8 | DN10 | DN15 | DN20 | DN25 | DN32 | DN40 | DN50 | DN65 | DN80 | DN100 |
| OD (French size) | 13 mm | 17 mm | 21 mm | 27 mm | 34 mm | 42 mm | 49 mm | 60 mm | 76 mm | 90 mm | 114 mm |
Stainless steel lock nut: frequently asked questions
Does the lock nut seal the joint?
No. It locks a position, but does not make the assembly watertight on its own. Provide sealing separately.
Which spanner for this lock nut?
An open-ended or adjustable spanner sized to dimension B across flats in the table: for example 31 mm at 1/2" and 45 mm at 1".
BSP or NPT thread?
BSP to ISO 7-1: Rp parallel tapped thread, for use with an R taper male thread. This lock nut is not compatible with NPT.
316 or 304 stainless steel?
This lock nut is 316 (CF8M). Unlike 304, 316 contains molybdenum and has better resistance to chlorides.
The appearance of the part may vary depending on the batch in stock. Contact us for confirmation.
See also
Full range: all stainless steel BSP fittings
Other stainless steel fittings: stainless steel male/male nipple, stainless steel male/male pipe nipple, stainless steel female/female coupling.
Other materials: brass fittings, black malleable iron fittings.
Useful guides:
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