How to Measure an O Ring (with only basic tools) - YouTube
How to Properly Size an O-Ring | Global O-Ring and Seal
How to Measure an O-Ring - Hi-Tech Seals - YouTube
O-Ring Sizing Tools - YouTube
O-Ring Tapes, O-Ring Tape for measuring the inside diameters of o-rings and other soft walled parts, manufactured by Pi Tape Corporation - Newman Tools