Kellner eyepieces were the most popular eyepieces for moderately wide field telescopic systems prior to the advent of some of the newer (and more expensive) designs. 3 element coated optics with field of view approximately 40 degrees and eye relief about 7mm. Fits standard 1-1/4" focusers. Metal barrel with knurled finger grip, and threaded for filters (thread is courser than that used for standard eyepiece filters, but ID is slightly larger. Put a little masking tape over the outside thread of your filter and it will screw in nice and secure). 10mm focal length. Plastic container included. Unused and a great value.