1
Conical spring
The washer is slightly dished. Tightening the bolt flattens the cone, which then pushes back like a spring, applying force all the way round, 360°, under the bolt head or nut.
2
Radial serrations
Fine ribs on the top face grip the underside of the bolt head or nut, adding resistance to rotation so the fastener is less likely to back off.
3
Preload that lasts
If the joint settles, the surfaces bed in or the temperature changes, the spring action takes up the slack and keeps tension on the bolt instead of letting it go slack.
Not sure which locking washer your joint needs? Send us the bolt size, property class and application and we will help you choose.
Click an industry to see how these washers are used.
What is a contact lock washer?
A contact lock washer is a serrated conical spring washer made to the French AFNOR standard NF E 25-511, also known as a contact washer or rondelle contact. It is slightly dished and has fine radial serrations on its top face. When the bolt is tightened the cone flattens and stores an elastic preload, and the serrations grip the bolt head or nut, so the joint stays tight under vibration, settling and temperature changes. Excel Trading Corporation supplies contact lock washers in SS 304 and SS 316 stainless steel, in series N, M and L.
How does a contact lock washer stop bolts from loosening?
It works in two ways. First, its conical shape acts as a spring: when the bolt is tightened the washer is flattened and pushes back evenly around the full 360° of the bearing surface, which keeps tension on the bolt if the joint settles or expands and contracts with temperature. Second, the radial serrations on its top face grip the underside of the bolt head or nut and add resistance to rotation. Together these help the fastener keep its preload under vibration.
What is the difference between series N, M and L contact washers?
The series sets the outer diameter and thickness of the washer for a given thread. Series N (narrow) is for socket head cap screws up to property class 8.8 and for counterbored holes. Series M (medium) is the standard series for hexagon head bolts and nuts in property classes 8.8 and 10.9. Series L (large) has the widest outer diameter, for slotted or oversize holes and soft bearing surfaces such as aluminium and plastics, with bolts of class 6.8 and 8.8.
Which way up should a contact washer be fitted?
Fit the contact washer with its serrated top face towards the bolt head or nut, the part that turns during tightening, so the serrations can grip it. Use one washer under each turning head or nut, do not stack contact washers, and tighten to the full specified torque so the cone flattens and the spring preload is created.
Is a contact washer better than a split spring washer?
A contact washer bears evenly around the whole bolt head through its conical shape and keeps a spring preload on the joint, and its serrations add resistance to rotation. A split spring washer bears mainly at its cut ends and offers limited protection against self-loosening in modern high-strength bolted joints. For joints with very severe vibration or dynamic loads, a wedge-locking washer such as Nord-Lock gives the highest security.
Is a contact washer the same as a Belleville disc spring?
No. Both are conical, but they are different products. A contact washer to NF E 25-511 is a serrated conical washer designed to sit under a bolt head or nut and keep a bolted joint tight. A Belleville disc spring is a precision spring element made to separate spring standards and is used to provide a defined spring force in mechanisms and spring stacks. For locking bolted joints, specify NF E 25-511 contact washers.
Should I choose SS 304 or SS 316 contact washers?
SS 304 (A2) contact washers suit most indoor and normal outdoor applications such as electrical panels, enclosures and machinery. SS 316 (A4) contact washers contain molybdenum, which gives better resistance to chlorides, salt spray and chemicals, so they are preferred in marine, coastal, food, pharmaceutical and chemical plant applications. Match the washer to the bolt material, A2 with A2 and A4 with A4.
Where can I buy contact lock washers in Bangalore or India?
Excel Trading Corporation supplies NF E 25-511 contact lock washers in series N, M and L, in SS 304 and SS 316, from Bengaluru to customers across India. Use the Request a Quote button on this page, call +91 7204435253 or email info@exceltrading.in with the thread size, series, material and quantity you need.
