Washers
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Frequently asked questions
How do ISO 7089 and ISO 7093 flat washers differ?
ISO 7089 is the normal series flat washer, while ISO 7093 is the large series with a noticeably bigger outside diameter. Large washers suit oversized holes, thin sheet and soft materials such as wood or plastic. Both come in hardness grades such as 200 HV or 300 HV for high-strength bolts.
Do split lock washers actually prevent loosening?
Transverse vibration tests show that split lock washers (DIN 127) do little to prevent self-loosening in a properly tightened joint, and DIN 127 has been withdrawn. For vibrating joints, correct preload, prevailing torque nuts, threadlocker or wedge-locking washer pairs are more effective.
Can a standard washer be used with a class 10.9 bolt?
It is not recommended, because a soft washer embeds under high clamp load and preload is lost over time. High-strength bolts need hardened washers, for example 300 HV to ISO 7089. For structural steel, use the washer specified with the structural bolt assembly.
How should washer material be chosen to avoid corrosion?
Match the washer material and coating to the bolt and nut, so an A4 stainless assembly gets A4 washers. Pairing zinc-plated steel washers with stainless bolts makes the washer rust first. Plastic or nylon washers are used where electrical isolation or protection of painted surfaces is needed.
How do wedge-locking washers work?
A wedge-locking washer is a pair of halves with angled cams on the inner faces and serrations on the outer faces. The cam angle exceeds the thread helix angle, so any loosening rotation increases clamp tension instead. They perform well in transverse vibration tests and can be reused while the serrations are intact.
What are conical spring washers used for?
Conical spring washers (Belleville type, DIN 6796 for bolted joints) act as a stiff spring. They compensate for embedding and thermal expansion, maintaining preload when clamped layers settle or a soft gasket is present. Typical uses are electrical busbars, gasketed flanges and assemblies under thermal cycling.
When are taper washers used?
Taper washers are used where a bolt passes through a sloped flange, such as the inner flange of a channel or I-beam. The taper compensates for the slope so the bolt head and nut bear flat, avoiding bending in the bolt. Choose the taper to suit the section, usually 8 or 14 percent.
When are plastic or fiber washers used?
Nylon, PTFE or fiber washers are used for electrical insulation, protecting painted surfaces and separating dissimilar metals. They also give light sealing on drain plugs or low-pressure fittings. Do not use them in joints that must hold high preload, as plastic creeps over time.
