Rubber Eyecup | Ocular Lens Extender Cover Outer Diameter: 38-48 mm

Look, it's a eye piece made of rubber for your scope. Maybe you want it to block light. Maybe you're like my father who for his entire life had a terrible habit of jerking his 30-6 when hunting and target practice and has the scars between his eyes to prove it. I got this for him the other week. But I have used them in the past and there's not much more to say here. These things work but they aren't for everybody. I wasn't too impressed with the build I was expecting something... more solid. But I supposed more solid defeats the purpose of the product so whatever lol

I found installation and use to be a bit cumbersome. The eye fit can be a little tricky centering the scope objective to your eye socket. This may take a bit of getting used to, but has potential. Great for keeping sunlight in check.

When pressing against my eye like at all, the outside edge flips over like a dog's ear and stays there.Rubber is very soft.

This is a bit larger than I expected. It works, but it's large and bulky. If it was shorter, and the eye cup was smaller, it would be great!

Fits the scope easily and securely. Extends the length of eyepiece. Great for bright shooting environs. For me, where I shoot is over lit by a bank of flourescent lights that really impede the scope picture. This stopped that totally. Plastic is meh. But it works.