In an attempt to provide some mediation, the original question is not ridiculous as, although I may never have used a regular rubber washer out of my seals box for, say, the connection on a gas hob (and we all lose those from time to time don't we!), now I will think at least twice before I look there for a gas washer. And to be fair if I was going to consider using an alternative I wouldn't have the time to post a question here and wait for a credible answer. Yes, those of us who are competent should dissaude those who ask questions which betray a total lack of any ability from even lighting the gas oven, but sometimes these seemingly silly questions raise points which will make professionals stop and think. That is why I am on here. If I ever kill anyone with poor gas work it is more likely to be a scenario I had never considered rather than shoddy workmanship.