To protect the damper shaft, this dust cover is mounted on the cap. This prevents dust and other dirt from fouling the shock shaft.
If this tube or cap is not mounted, there is a good chance that dirt collected during rebound and compression will damage the shock seals, causing leaks.
Note: There are many reproductions available that are poorly finished and designed. They look like the original but differ in many details. The one mentioned here is not only identical to the original in every detail, but the hardness of the plastic is also identical.
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