Slack prevention washers

Lock tab washers are often fitted to brake and suspension components to help prevent a bolt or nut from loosening. The ends of the washer are bent over and against the flats of the fastener to lock it into place and remove any possibility of it turning, although some means of stopping the entire washer from moving is required – it will be bent over something else as well, or a single tab washer will secure two or more bolts.

Shakeproof washers (sometimes called star washers) can be fitted where a nut or bolt may be subject to excessive vibration. The jagged edges of the washer help to dig into the nut or bolt and whatever it is fitted to. This is useful for earth straps, helping to cut through paint and achieve a good connection to the metal beneath. External teeth can provide more grip than teeth around the inside of the washer.

Flange nuts look like a combined nut and washer, but are made as a single piece and so the flange will not rotate on the nut. ( You can get nuts with an integral washer that will rotate, but they are called SEMS units.) Flange nuts may or may not have a serrated face which helps to reduce the risk of the nut slackening, but whether or not you want that depends on the surface to which it is being applied – it could damage aluminium or plastic for example, especially if it is used in a position that needs to be removed regularly. A flange nut acts like a combined nut and washer, so a washer isn’t required.

A spring washer helps to reduce the risk of a fastening from loosening by providing some resistance. It used to be the case that a spring washer would be used on top of a flat washer, but testing machines have come out over the last 10 or 15 years that show the nut is less likely to unwind if it is used with only a spring washer. This could be a problem if the flat washer was needed to spread the load, but you can get around this by using what are called rectangular profile spring washers. These are also more robust than the cheaper square-section washers, which might spread out of round as you tighten the nut if they are particularly weak.

Tab washers are bent over a fastener to stop it unwinding, but have to be anchored at the other end to stop the washer turning.

Shakeproof washers may have the teeth facing inwards (in which case they are hidden from view in use) or outwards.

The rectangular profile spring washer on the right is less likely to spread under tightening than the square-section one on the left.

Even when it comes to flat washers, there is a wide range of thicknesses and diameters available. All of these are for an M10 bolt.

Flange nuts look like a combined nut and washer. They may or may not have teeth on the flange face for extra grip.