Astro-Physics AP Solar filter, external diameter is 180mm and thread side diameter is 171-172mm. I believe it is for 6" scope and typical AP quality with solid ring.
Filter front surface (facing sun) is good (1st 2 picture)Filter inner surface (facing scope) got some spots and previous owner covered/patched up with black paint to block direct sun light penetration. I tested through and didn't see any light escape from those patch up holes.
Due to defects, selling very cheap. User is advised to inspect thoroughly before use for own safety
Filed under: Eyepieces & Accessories