Thank you for your replies, Gentlemen. I had looked at the Polly catalogue but did not find it in there. I will give them a ring today and get some in. The reason the last one broke is that at full heat the drain cock went really tight. On trying to open it the bottom fitting turned and cracked the glass. I think I am very lucky that disaster did not ensue. We aborted the steam test at that point and I came home rather sadder than I was an hour previously, when it had passed it's hydraulic test. Oh well, that's life 