Following some careful investigation I've decided to use stainless grade A4 ie 316 for securing various bits to my latest boiler. A4 is a good deal less suspectible to chloride embrittlement than the usual A2 304 stainless but more expensive. I bought them from www.a2a4.co.uk. The cost from them was slightly less than buying ordinary steel ones from well known ME suppliers and just a quarter of the quote I got from a well known supplier of fasteners based near London. I didn't try another well known supplier based in the west. MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.