Lock Nut

Description

A proper threaded seat, welded where you need it

Cutting a hole in a manifold and hoping for the best is how you end up with a leak that whistles at idle and throws a fault code. This lock nut gives you a machined M18 x 1.5 thread you can weld exactly where you want it, so a sensor, probe or plug screws in square and seals against a flat, purpose-made face.

M18 x 1.5 is the thread the manufacturers use for oxygen and lambda sensors across nearly every petrol vehicle on the road, which means whatever you are fitting will almost certainly thread straight in without an adaptor.

Stainless, because the alternative seizes

Mild steel bungs rust from the inside out. A year or two later the sensor is welded into the thread by corrosion and you are drilling it out, usually damaging the manifold in the process. Stainless holds its thread through heat cycling, coastal humidity and years of road grime, so the sensor still comes out with a spanner when you need to replace it.

It welds cleanly to stainless, aluminised and mild steel pipe with MIG or TIG.

Common uses

• Adding an oxygen or lambda sensor position to a custom manifold or header
• Fitting a wideband sensor for tuning and datalogging
• Mounting an EGT probe on a turbo manifold or downpipe
• Blanking off a redundant sensor hole after a decat or manifold change
• Repairing a stripped or corroded factory sensor thread

Specifications

Fitting it

Drill or hole saw the pipe slightly undersize and dress the hole so the nut sits flush against the curve. Tack it in three or four places first and check your sensor threads in freely before you run the full weld, because heat distortion in the thread is far easier to prevent than to fix. Anti seize on the sensor threads on final assembly is still worth doing.