Unfortunately, this acoustic boot 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

Acoustic Boot for Roberts-Gordon vacuum pump models:

• EP-200
• EP-201
• EP-203

Boot Only:

• 4.5" x 4.5" x 8"
• High Temperature silicone rubber
• Wire reinforced

• Replaces:
  
  • 91411901 (Black boot)
  • 1085-4580

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.