Lock Nut Galvanized Malleable Iron

The hot-dip galvanized malleable cast‑iron locknut (backnut) is an essential plumbing part for clamping and securing assemblies. Its purpose is not to seal, but to lock and secure a male threaded fitting against the wall of a tank, vessel, manifold, or wall plate.

What is this locknut used for?

The locknut—also called a jam nut—securely fixes a fitting passing through a thin wall. Once the primary fitting (bulkhead, wall outlet, etc.) is installed with its sealing gasket, the locknut is tightened on the opposite side of the wall to hold it firmly in place and prevent loosening due to vibration or handling.

Example uses: Fix a tap outlet through plasterboard, secure a fitting on the wall of a hot‑water cylinder or rainwater tank.

Technical Features (EN 10242 Compliance)

Manufactured to European standard EN 10242, a mark of reliability and quality for pros and demanding DIYers. The standard guarantees precise characteristics:

• High‑Quality Material: White‑heart malleable cast iron (grade EN‑GJMW‑400‑5 to EN 1562), known for high mechanical strength under pressure and impact.
• Superior Anti‑Corrosion Protection: Hot‑dip galvanized finish with a zinc layer around 70 µm. This advanced protection ensures excellent service life, even in damp or corrosive environments.
• Precision Thread: The female thread is parallel gas thread (G), compliant with ISO 228‑1 (BSPP), for smooth make‑up and effective locking on the corresponding male thread.

Installation Tip

Remember that sealing is done by the primary fitting (using a flat gasket, hemp, resin or PTFE tape). The locknut is fitted last to complete the mechanical fixing.