Safety / Vibration-Lock Washer

How Nord-Lock wedge lock washers work

A Nord-Lock washer is a pair of washers, pre-glued together, with matching cams on the faces that meet and radial serrations on the outside faces. When the bolt is tightened, the serrations grip into the bolt head or nut on one side and the clamped part on the other, and the cams lock together. Because the cam angle is greater than the pitch of the thread, any turn in the loosening direction has to ride the cams up, which stretches the bolt and increases the clamp load: a wedge effect that stops the bolt rotating loose. Nord-Lock describes this as securing the joint with tension instead of friction.

Nord-Lock's Wedge-Locking Solutions brochure reports a Junker vibration test (DIN 65151) on an M8 8.8 bolt with a 25mm clamp length, in which the joint with Nord-Lock washers kept its clamp load, while the clamp load with a nylon inserted nut, a split ring washer or a plain nut dropped sharply. These are the manufacturer's test results, not a load rating for a joint.

Standard Nord-Lock washers: Delta Protekt, stainless and SC

Standard Nord-Lock washers are the original flat wedge-locking pairs, without the X-series cone, and come in more materials and sizes. Nord-Lock's material guide for them:

• •Delta Protekt steel (EN 1.7182, through hardened, zinc flake coated): general steel applications, bolts up to class 12.9, -50 to 200°C. M3 to M72 and 1/4 to 1 inch, plus Delta Protekt black in M6 to M24.
• •316L stainless (EN 1.4404): general stainless steel applications in non-chlorine and non-acid environments, bolts up to A4-80, -160 to 500°C. M3 to M48 and 1/4 to 1 inch.
• •SMO 254 stainless (EN 1.4547): salt water applications, pumps, chloride environments, heat exchangers, desalination, food processing and medical equipment, bolts up to A4-80, -160 to 500°C. M3 to M36 and 3/4 inch. The choice for coastal and marine joints.
• •Inconel 718: high temperature applications such as gas turbines, turbo chargers and incinerators, -160 to 700°C. M16.
• •SC washers (Delta Protekt, EN 14399 K2), M12 to M36: made for EN 14399 K2 structural bolting sets in 8.8 HR (and HV) assemblies, replacing the standard EN 14399 washers, so Nord-Lock says the tightening torque must be adjusted to the HR bolt guidelines. Nord-Lock does not recommend them with chamfered plain washers, and through holes take two pairs. Use them only where the bolting designer specifies them.
• •Assortment kits of 100 washers in Delta Protekt or 316L stainless.
• •Hardness: the mating surfaces must be softer than the washers, or the serrations cannot grip.

Nord-Lock X-series: wedge locking with a spring

The X-series washers on this page add a conical, disc-like shape to the wedge-locking pair. Hobson says the cone maintains tension by compressing and springing when required, and Nord-Lock says the added spring effect compensates for loss of preload due to slackening; Hobson adds relaxation and settlement. They suit joints with short clamp lengths. Hobson lists rail and trains, wind turbines and motors as applications.

• •Material: through hardened steel (EN 1.7225 or equivalent) with a Delta Protekt zinc flake coating, which Nord-Lock states endures a minimum of 600 hours in the salt spray test (ISO 9227) and introduces no risk of hydrogen embrittlement.
• •Bolts: Nord-Lock lists X-series washers for bolt grades 8.8 and 10.9, and a temperature range of -40 to 150°C.
• •Thread: designed for metric and UNC coarse pitch. They can be used on fine pitch threads, but Nord-Lock warns the larger difference in pitch raises the tension and the untightening torque, which can take the bolt past its elastic limit.
• •Large OD (sp) washers: an enlarged outside diameter for large or slotted holes and soft surfaces, used with a flanged nut or bolt to spread the load.

Nord-Lock X-series washer sizes

Every X-series washer we carry, smallest to largest. The size is the bolt the washer fits; some metric sizes also suit an imperial bolt (M8 with 5/16 inch, M14 with 9/16 inch, M16 with 5/8 inch).

When not to use Nord-Lock washers

Nord-Lock does not recommend its washers (original and X-series) when the mating surfaces are not locked in place, when the mating surfaces are harder than the washers, on very soft surfaces such as wood or plastic, where there will be extremely large settlement, or on joints that are not preloaded. Hobson's anti-vibration paper makes the same point for all ramp and serrated locking washers: they only work while there is tension in the joint.

A locking washer stops a correctly tightened bolt from coming loose; it does not make the joint stronger. Hobson and Nord-Lock publish locking test results and installation torques, not load ratings for a joint. For structural, lifting, suspension or other safety-critical joints, use the bolts, nuts and washers the engineer or equipment maker specifies.

Schnorr safety washers: Type S and Type VS

A Schnorr safety washer is a single washer shaped like a disc spring, with a trapezoidal cross-section and serrations on both sides. Schnorr says it combines security through friction with mechanical locking, and that its outside diameter is matched to the head of a socket head cap screw (DIN 912 / ISO 4762), so it sits neatly under them. Schnorr's brochure reports Junker tests (DIN 65151) in which joints with its safety washers kept their pretension after 2,000 cycles.

• •Type S: the standard washer, which Schnorr makes for M1.6 to M36 screws in property classes up to 8.8. We carry M2 to M36.
• •Type VS: the same inside and outside diameter and serrations as Type S, but thicker (see the table), for 8.8 to 10.9 bolts from M5 to M30. Schnorr also lists Type VS for slotted holes.
• •Clearance holes: fit a safety washer on both sides, under the bolt head and under the nut.
• •Fitting: Schnorr recommends not using them with a flat washer, not fitting them upside down and not stacking them.
• •Finishes: plain and zinc plated spring steel, and 304 stainless. Zinc plating is for indoor, low corrosion work; use the 304 washers outdoors.
• •Torque: Hobson's Schnorr tightening torque sheet gives non-binding approximate values by bolt grade and finish; ask us for a copy.

Nylon anti-loss washers

Nylon anti-loss washers (M3 to M8) are small natural nylon washers that push over a screw thread to keep the screw from dropping out of its hole when a panel or part is removed. They do not lock the screw. Neptune 316 flat washers are on the flat washer page.

Fitting Nord-Lock washers

1. Fit the pre-glued pair on the bolt with the cam faces together and the serrated faces out, oriented as Nord-Lock's instructions show. Nord-Lock notes the glue only holds the pair together for the first fitting. (These steps are from Nord-Lock's X-series user manual.)
2. Tapped hole: one pair under the bolt head. Through hole: two pairs, one under the bolt head and one under the nut. On stud bolts, a pair under the nut.
3. Lubricate the thread and the area under the head (and the nut on through bolts), as Nord-Lock recommends.
4. On through bolts, turn both the bolt head and the nut first so the cams on both pairs close, then hold one while you tighten the other.
5. Tighten to the torque for the clamp load the joint needs, with a calibrated torque wrench.

Nord-Lock X-series torque examples

Nord-Lock publishes the values below as configuration examples verified in its test laboratory. It says they are indicative and should not be seen as recommendations, because conditions, joint designs and requirements vary; Nord-Lock offers free torque calculations for a specific joint.

Can Nord-Lock washers be reused?

Nord-Lock's X-series manual says the washers can be reused, and that reusability depends on the conditions of use. Inspect the cams and serrations for obvious damage before refitting, and always refit them in pairs, cam face to cam face. Nord-Lock notes its lifetime warranty does not apply to reused washers, and the laser marking (brand, control number and type code) is for identification and will not last if the washers are reused.

Nord-Lock washers in Adelaide

Allmat supplies Nord-Lock washers, Schnorr safety washers, bolts and nuts to maintenance crews, fitters, mechanics and trade across Adelaide and South Australia. Add the washers to a quote with the bolts and nuts they go on, and we will price the lot.

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