Rubber eye piece is missing from 20mm still works perfect. You can also use rubber from 10mm. Product is a set of two Celestron telescope eyepieces, one 20mm and one 10mm, both with a 1.25-inch diameter. These eyepieces are designed specifically for Celestron telescopes and are lightweight, making them easy to handle during use. Perfect for astronomy enthusiasts looking to explore the night sky with increased clarity and precision, this eyepiece set offers a rare opportunity to enhance your observing experience.