KF40 compatible catcher ring for vacuum chambers

A custom centering ring that can be used for mating KF40 flanges for simple vacuum chamber ports. Pumping is ensured via four venting holes. The external Buna-N o-ring should measure 40.64 x 5.3 mm (ID x cord thickness). It requires an internal 16 x 3 mm FKM 80A o-ring to secure a 5 mL Eppendorf tube in the cetral hole.