4 Inch Minor Axis Secondary Mirror. I gently cleaned it once. I used it for a little Heliostat mirror. Previous owner said it was never cleaned and was 1/10 PV WFE. I do not have documentation or know if that is true but it looks good and performs well. 7/8" thick. Coating in excellent condition. $135 firm shipped CONUS. Prefer payment by Money Order. Sorry, I don't do PayPal. Please note my Astromart rating. Thanks for looking.