Guide to Vulcanized O-Rings - Arizona Sealing Devices, Inc.
First, locate the splice joint on the vulcanized O-ring. Using your fingers, give it a slight twist in either direction. Do so gently, or the O-ring may break. Also avoid bending the O-ring at the joint to avoid breakage. Provided that the vulcanized O-ring passes this "twist and tug" test, it is safe for installation or continued use.