Unfortunately, this neoprene ring is no longer available as a separate item. Here is the link to the Acoustic Boot kit which comes with the rings:

Acoustic Boot Kit

Neoprene Ring for Roberts-Gordon models:

• CoRayVac^® CRV B Series
• CoRayVac^® CRV E Series
• CoRayVac^® CRV A Series
• CoRayVac^® CRV 6-60
• CoRayVac^® CRV 5-40 (only when 4'' OD tubing is used entering the vacuum pump)
• CoRayVac^® CRV 4-40 (only when 4'' OD tubing is used entering the vacuum pump)

Details:

• 4.5" ID, adapts acoustic boot to 4" OD tubing entering vacuum pump

Roberts-Gordon, LLC original parts. Roberts-Gordon, the world leader in infrared heating, headquartered in Buffalo, NY. With an extensive representative network in the United States, Canada, and across the world.