| http://www.w3.org/ns/prov#value | - The hollow ring 53 comprises a light-weight material, including, but without limitation, polymeric materials such as polyester, vinyl ester, epoxy, polyimide, polyamide, polypropylene, and/or PEEK. In one aspect, the hollow ring 53 may comprise a composite material of fiber-reinforced thermoplastics or fiber- reinforced polymers.
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