The design has now been simplified by using a schedule 40 PVC 1.5" coupling (about $1.00 at any hardware store). Just cut 7/8" of one end, using a miter box. The metal plate is epoxied to the PVC, rough the surfaces with some 240grit sand paper first. The second metal plate is not needed now that the diameter of the ring is smaller.
The filter ring should screw itself into the plastic. If not just warm the edge of the ring to the point of flexibility.
Rolf
