1. Bail jars need 3 pieces to function: the jar, the rubber gasket and the glass lid. The jar and lid must be without chips and the gasket should be free from weak spots or cracking. I buy boxes of gaskets from Kidron Town and Country store but Lehman's also sells them.
2. After jar is filled, using recommended head space, wipe any food residue from the jar and stretch the gasket over the mouth of the jar. There will be a "shelf" that the gasket rests on. Make sure that the gasket is flat and not twisted.
3. Place glass lid over gasket and put bail closure in place.
4. Process for recommended time and allow to rest on the counter for 24 hours and then check seal. To check seal you remove the bail closure and pick the jar up by the lid. The picture shows me checking the seal on a jar of blackberries. Hold the jar only an inch or two above the counter to avoid a broken jar in case it didn't seal.
I only use my bail jars for foods that are canned with the boiling water bath method, I don't use them in my pressure canner. Certain foods need to be pressure canned to kill any botulism spores, but foods canned with a water bath canner aren't prone to botulism. Food spoilage will generally unseal the lid from previously sealed jars, look funky and/or smell bad, any of these will be obvious in a regular canning jar and will be equally obvious in a bail jar. Observing proper safety measures can make using these vintage jars a rewarding experience and less like a death defying act by a crazy women who enjoys flirting with death. :-D