[rhysdad]

I use Le parfait/Kilner type jars with the spring lid. I wash and dry thoroughly then sterilse in the oven for 5 minutes at 100°c. I use the rubber seals time and again and, so far, have had no problems whatsoever. I don't invert either!

[catllar]

I'm an inverter. I put the jars and screwtops in the oven before filling, then do them up and turn them upside down until cool. There's often a gap at the bottom of the jar, but as the hot jam has sterilised the space and gravity will pull it down again eventually to fill it up I don't worry. Saves having to faff with discs, rubber rings and it works for me. Each to their own, and the jam lasts happily from one year till next harvest. I guess it's not acceptable for people who are going to show their jam, however!