Just finished making this sunfilter for my Dad's scope. Of course, can't even test it at the moment, too many clouds! Hopefully I will get to test it tomorrow.
Made from laser cut rings of 6mm MDF (courtesy of my brother), mostly glued together, the front one screwed on.
Made something of a sight for it as well.
The notches slip over screws and the whole lot twists, making it very secure.