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Does a Lock Washer Go on Before a Flat washer
In mechanical fastening, washer installation order affects load distribution, surface protection, and resistance to loosening. A common question is whether a lock washer should be installed before a flat washer. In standard assembly practice, the answer is no. The flat washer is usually placed directly against the surface, and the lock washer is placed between the flat washer and the nut or bolt head.
Standard Washer Installation Order
The most common arrangement is:
Bolt head → flat washer → mounting surface → lock washer → nut
In some assemblies, the lock washer may also be placed under the bolt head instead of under the nut, depending on the design. However, the main principle remains the same: the flat washer should contact the surface first.
What a Flat Washer Does
A flat washer is designed to spread the clamping force over a larger area. This helps protect the surface from damage and reduces localized stress. It also improves the stability of the connection, especially when the material is relatively soft or when the fastener hole is oversized.
Common examples include m10 washer, m3 washer, 1 4 washer, 1 4 flat washer, 3 8 flat washer, m12 flat washer, 6 flat washer, and m16 flat washer. No matter which size is used, the function of the flat washer remains the same.
Main Functions of a Flat Washer
Distributes load evenly
Protects the mounting surface
Reduces indentation and wear
Improves joint stability
What a Lock Washer Does
A lock washer is used to help resist loosening caused by vibration or movement. It works by adding spring tension or friction to the assembly. To do this effectively, it needs to be positioned where it can act directly against the turning part, usually the nut or bolt head.
If the lock washer is placed directly against the mounting surface, it may scratch or damage that surface and may not provide the intended locking effect.
Main Functions of a Lock Washer
Helps reduce loosening under vibration
Increases friction in the joint
Supports fastening reliability in moving assemblies
Why the Washer Order Matters
The washer order is not just a detail. It directly affects how the joint performs over time.
When Installed Correctly
When the flat washer is placed first, it creates a smooth bearing surface and spreads the load. The lock washer then acts against the nut or bolt head to improve resistance to loosening. This combination allows both washers to perform their separate functions properly.
When Installed Incorrectly
If the lock washer is placed against the surface before the flat washer, several problems may occur:
Surface damage from the lock washer edge
Reduced load distribution
Less effective locking performance
Increased risk of loosening over time
Common Washer Materials
Washers are available in many materials, depending on the application environment. Among them, stainless washers are widely used because they offer good corrosion resistance and long service life.
Stainless Washers
Stainless washers are suitable for humid, outdoor, or corrosive environments. They are commonly used where both durability and clean appearance are important. When paired with the correct installation order, stainless washers can support stable fastening performance for a wide range of assemblies.
Metric and Imperial Washer Sizes
Both metric and imperial washer systems follow the same installation principle.
Metric Washers
Examples of metric washers include:
m3 washer
m10 washer
m12 flat washer
m16 flat washer
These are commonly used in machinery, equipment, and structural assemblies.
Imperial Washers
Examples include:
1 4 washer
1 4 flat washer
3 8 flat washer
6 flat washer
Even though the measurement standards differ, the flat washer should still go against the surface first.
Practical Assembly Guidance
When assembling a bolted joint, it is important to check the washer size, material, and placement before tightening.
Basic Guidelines
Place the flat washer directly against the mounting surface
Position the lock washer closer to the nut or bolt head
Match the washer size to the fastener size
Use stainless washers when corrosion resistance is needed
Confirm whether the design calls for one washer or multiple washers
Conclusion
The answer to the question is straightforward. A lock washer does not normally go on before a flat washer. The flat washer should be installed first against the surface, and the lock washer should be placed between the flat washer and the nut or bolt head. This order helps protect the surface, distribute load evenly, and improve resistance to loosening.
Whether the assembly uses metric washers, m10 washer, m3 washer, 1 4 flat washer, 3 8 flat washer, m12 flat washer, 6 flat washer, m16 flat washer, or stainless washers, the same basic principle applies. Correct washer placement supports a more stable and reliable fastening connection.
