2 Pack Google Cardboard Bi-convex Biconvex Lens Set - 2 Pair Of High Quality 25mm Diameter 45mm Focal Length for Google Cardboard Cut Out DIY Virtual Reality Headset (VR) Play around with virtual reality without spending an arm or a leg on an Oculus Rift, an HTC Vive, or one of those VR players rich kids beg their parents to buy them. Because these lenses are manufactured to Googles specs (25 MM diameter and 45 MM focal length for generation 1) you can slap these bad boys in your Google Cardboard and start tripping over that bear behind you. In addition to home made VR headsets like Google Cardboard, you can use these lenses for a classroom science project or other application. Maybe turn them into mini magnifying glasses to experiment with focusing sunlight? Each package includes 2 pairs of lenses so you can pretend you didn't break the first pair trying to get things together. Not that they'll break easy, but people get creative and do incredible things.