Alps Pacino

As Paul said "dust seals" are actually for us termed "corrosion seals"

They are generally placed on a cast caliper with chrome plated pistons to stop rust and corrosion over a period of time.

If you have an alloy caliper and stainless steel piston there is nothing to rust or sieze over time so not strictly necesaary.

However because its difficult to get people to understand this some of the new bigger range (not yet released) have been fitted with rubber seals. They are totally pointless but will stop some of the associated stigmatisms of race calipers.