Kyosho 1-N4055N M4x5.5mm Nylon Lock Nut 5pcs

A pack of five M4 nylon insert lock nuts, 5.5mm in height, from Kyosho's universal hardware range.

A nylon insert nut has a collar of nylon moulded into its top. As the screw threads on it cuts into that nylon, and the friction created is what stops the nut backing off under vibration. M4 nuts appear where loads are high, which on most cars means wheel nuts, engine mounts and main chassis fixings, and those are exactly the positions where a fastener working loose has serious consequences.

They are consumable by design. Every removal and refit cuts the nylon further, and after a few cycles a nut that spins on by hand has stopped doing its job. Reusing tired lock nuts is how a wheel comes off mid-run, which is the one failure that ends a race and often the car with it.

The 5.5mm height includes the nylon collar, so check clearance where space is tight.

Five are supplied. Given how cheap they are relative to what they hold on, replacing rather than reusing is the sensible policy. This supersedes the older Kyosho number 1179.