This replacement Silicone Seal is designed for all Aclaim®2 (HC401) and FlexiFit™ 405 (HC405) Nasal CPAP/BiPAP Masks. The Silicone Seal is available in two sizes: Small and Large. Aclaim2 and FlexiFit™ 405 masks use a single frame size so either Silicone Seal size can be used regardless of the size currently being used on your mask. Recommended Replacement Schedule: Twice every month.