What are these rubber rings on my brake caliper bolts for? I have purchased a disc brake adapter which came with a set of mounting bolts for mouting the adapter and the caliper together. The bolts have a rubber ring on them, but I'm not sure what it's for. Should it be mounted together with the caliper and adapter, or is it just for holding the washers and shims in place as part of the packaging?
The bolts have a rubber ring on them, but I'm not sure what it's for. Should it be mounted together with the caliper and adapter, or is it just for holding the washers and shims in place as part of the packaging?


The rubber rings are just for holding the washers and shims in the right place and should not be installed on the bicycle.



There are many disk brake adapters. Without a description of what you have I could not find instructions specific to your situation. The pictured adapter is similar to yours (it's a SM-MA-F180P/P2) and shows no rubber rings.

Added information after the part make and model was identified:
The manual for the Tektro A12 lacks an exploded diagram or words describing the washer arrangement.
Frequently asked questions on their site does not cover this.
Their videos have a how to install a caliper part but they don't show the washer arrangement.
You can try their contact page.  

Often the correct way to install something becomes clear once the part is installed. Since Shimano has a similar bolt/washer setup try it without the rubber ring first.