Things I liked:This is simple diopter rear sight. Appears to be well made for the price. It clamps up tight on a 11mm / 3/8" rail. Item is made in China. Things I would have changed:It does not have a locking pin that would engage the countsunk holes on the rail of my air rifle to prevent it from sliding. The elevation, windage and rail tightening knobs are plastic. But they appear to be sturdy enough. It would be nice if the apperture size was adjustable. What others should know:This is installed on a Weihrausch HW50S which is about 40 years old. I wish I had bought the original German Diopter when the rifle was new in 1968. But this one appears to be OK for the purpose. This is a great improvement over the notch sight. Also with the hooded front sight at the end of the barrel you have a much longer sight radius making it much easier to hit the"X" ring on a 33 foot NRA air rifle target. This is a new purchase and I have only used it one day.