The Scuba Spec is a prescription lens insert designed for use in all single lens dive masks and full-face snorkeling masks. The Scuba Spec insert is not compatible with dive masks that possess two separate eye pieces. The anchor bracket of the #199EB Scuba Spec insert is attached to the inner surface of the mask's faceplate using the following methods: (a) 3M's Dual LockTM technology (included with purchase) or (b) application of silicone adhesive (not included with purchase). Installation of the insert using the Dual LockTM technology only takes minutes and does not require the purchase of silicone adhesive. The spectacle frame is made of durable nylon material. The Scuba Spec insert can accommodate any prescription power: single or bifocal vision. Non-prescription reading lenses can also be mounted in the Scuba Spec insert. If your optical prescription changes, you simply replace the lenses. There's no need to replace the dive mask or Scuba Spec frame. Purchase of the Scuba Spec insert does not include the optical lenses. Optical lenses can be purchased from www.spectacle-inserts.com or your local eye care professional. If you have difficulty obtaining your lenses locally, contact Prescription Spectacle Inserts Int'l at 803-292-6485.