Silca Hiro Chuck Elastomer Seal
The amazing Silca Hiro Chuck V.2 uses the a new, exceptionally durable and resilient high-pressure seal made from an elastomer. This gasket is called the 254 and is currently only utilized by the Hiro Chuck. Pro mechanics requested a gasket for the Hiro that could hold up for an entire year of pro team use (!) before needing replacement, and the 254 was Silca's answer. So you may not need to replace yours for many years, but it is always good to have one set aside for emergencies. Being prepared makes sense.