What is the DIN 988 Standard?
DIN 988 is a German technical standard that outlines the strict dimensions, tolerances, and materials for metric shim rings (fit washers) and supporting rings. Published to establish consistency across manufacturing, the standard dictates how these washers are produced to ensure exact spacing and precise mechanical adjustments.
While standard flat washers are designed simply to distribute the clamping force of a bolt, DIN 988 Shims are specifically designed to take up axial play, control end float, and accurately preload bearings.
The Core Anatomy of a DIN 988 Shim
A DIN 988 shim washer is designated by three strict metric measurements:
- Inside Diameter (d₁): Designed to fit snugly over a shaft or fastener location. Nominal sizes range widely, from tiny M3 configurations up to massive M170 industrial applications.
- Outside Diameter (d₂): Defines the total outer surface area, providing structured support against the adjacent housing or bearing face.
- Thickness (h): The absolute core feature of the shim. Thicknesses are precisely controlled and generally range anywhere from an ultra-thin 0.1mm up to 2.0mm or more.
Shim Rings vs. Supporting Rings
The DIN 988 standard actually categorises components into two distinct types based on the mechanical problem they solve:
- Shim Rings (PS Series): These have perfectly smooth contact faces. Their primary job is to bridge small physical gaps, remove axial play, and stop components from sliding back and forth along a shaft. They are typically stamped from carbon spring steel or stainless steel.
- Supporting Rings (SS Series): These are built to handle heavier mechanical abuse. They are placed against rounded or chamfered component edges to prevent structural deformation caused by severe axial forces. They feature higher material hardness (440 to 500 HV) and are typically machined with precise ground side faces, making them more expensive than standard shim rings.
Common Industrial Applications
You will find DIN 988 shims anywhere precision rotating motion is required. A few crucial use cases include:
- Gearboxes & Transmissions: Keeping gears perfectly aligned on their shafts to prevent premature tooth wear.
- Bearing Assemblies: Compensating for minor tolerances in bearing seats (e.g., standard crankshaft bearings like the 6305) to eliminate end-play.
- Electric Motors & Pumps: Controlling the magnetic centering and end-float of rotating armatures.
- Retaining Ring Support: Placed directly ahead of a circlip or snap ring to provide a perfectly square, flat surface for the retaining clip to bear against.
Please contact us today if you require assistance finding the right Shim Washer.
