The washer is probably the most ignored component in a mechanical assembly, yet its absence or improper use is a frequent cause of loose fasteners, damaged surfaces and unstable joints. In this guide we look at the main types and when to use each.
Flat washer (DIN 125 / ISO 7089)
The standard flat washer has a seemingly simple function: to distribute the load of the screw over a larger area, protecting the underlying material from the impression of the head or nut. It is actually essential when fastening on soft materials (aluminium, plastic, wood), when the hole is larger than necessary (the washer acts as a bridge), and to create a flat, smooth bearing surface for the nut.
Grower / spring washer (DIN 127)
The grower washer (or split lock washer) is an open, helically bent washer that exerts constant axial pressure under the nut. This pressure maintains tension in the fastener and reduces the risk of loosening under vibration. Note: Modern engineering studies have shown that the grower washer is less effective than traditionally believed. For critical applications under vibration, the self-locking nut (nylstop) is often a better choice.
Belleville / cup washer (DIN 6796)
The Belleville washer is a conical cup washer that acts as a spring. When compressed by the screw, it exerts a significant spring force that maintains preload even with small changes in joint length (thermal expansion, settlement). It is used in industrial applications where maintaining preload is critical: flange joints, fasteners on materials that settle over time, and high-temperature applications.
Wide washer (DIN 9021)
The wide washer has a significantly larger outer diameter than the standard washer. It distributes the load over a larger area and is indispensable for fastenings on very soft materials, thin panels or oversized holes.
Spacers
Spacers are hollow cylinders (metal, nylon or brass) that maintain a precise distance between two components. They find application in the assembly of PCBs and circuit boards (hexagonal M3 spacers), in separating planes in profile structures, and in creating spaces for cable routing or cooling.
Standard flat washer size table
|
Screw |
Inner diameter |
Outer diameter |
Thickness |
|
M3 |
3.2 mm |
7 mm |
0,5 mm |
|
M4 |
4,3 mm |
9 mm |
0,8 mm |
|
M5 |
5,3 mm |
10 mm |
1.0 mm |
|
M6 |
6.4 mm |
12 mm |
1,6 mm |
|
M8 |
8.4 mm |
16 mm |
1.6 mm |
|
M10 |
10,5 mm |
20 mm |
2.0 mm |
Washers and spacers at DHM-online
At DHM-online you will find flat washers, growers, Belleville and spacers in sizes M2 to M20, in galvanised steel and A2 stainless steel. Browse the Hardware and Fasteners section to find the type and size you need.
