An extra set of self adhesive sticky pads.
A set is four pads. These are made from high density Silicone rubber, with a highly adhesive, temperature resistant glue.
If you need to add pads to the top and bottom of your spacer bars, then you need an extra set. Handy when the device you are protecting does not have built in rubber boots, or the boots are not situated in the best place for your set up.