M3.5 x 50mm Raised Head Countersunk Electrical Screw - 100 Pack

The Knightsbridge M3.5 x 50mm electrical screw is a raised-head countersunk machine screw designed for fixing electrical accessories to metal back boxes and mounting frames. The 3.5mm diameter thread matches the standard fixing holes on UK switches, sockets, dimmer plates and other wiring accessories. The 50mm length accommodates deeper back boxes and provides sufficient thread engagement when fixing through thick cover plates or multiple mounting frames.

Used in residential, commercial and industrial electrical installations, these screws fit Knightsbridge metal accessories and most other UK manufacturers' products where the fixing hole is tapped for M3.5 thread. The raised countersunk head sits flush or slightly recessed when driven into a countersunk hole, giving a clean finish on visible screws where the accessory has recessed screw apertures. The nickel-plated steel finish resists corrosion in standard indoor environments and provides a silver metallic appearance that matches chrome and polished metal accessories.

Supplied as a 100-pack in a Knightsbridge polybag, the screws are typically used when installing multiple accessories across a single project or when building stock for maintenance and refurbishment work. The M3.5 thread is fine-pitch, providing better grip in the thin metal of standard electrical back boxes compared to coarser threads, and reducing the risk of stripping the thread when re-tightening accessories during redecoration or rewiring.

Product Specification Sheet

What electrical accessories do these screws fit?

These M3.5 screws fit UK switches, sockets, dimmer plates, fused connection units and other wiring accessories with standard M3.5 threaded fixing holes. They work with Knightsbridge products and most other UK manufacturers' metal and plastic accessories.

When would I need the 50mm length instead of a shorter screw?

The 50mm length is used for deeper back boxes (35mm or 47mm depth), when fixing through thick decorative plates, or when securing accessories onto multiple mounting frames. For standard 25mm back boxes with single plates, a 25mm or 35mm screw is typically sufficient.

Can these be reused if I remove an accessory?

Yes, the fine M3.5 thread allows screws to be removed and re-fitted several times without stripping the thread in the back box, provided they are not over-tightened. However, if a screw has been cross-threaded or the back box thread is damaged, replace with a new screw rather than forcing the old one.

Are these suitable for outdoor electrical installations?

The nickel-plated steel finish provides basic corrosion resistance for indoor use and dry outdoor installations such as garages and covered porches. For fully exposed outdoor accessories or marine environments, stainless steel screws are recommended instead.