A friend has asked me about some heavily rusted bolts that he needs to replace. They appear to be 12 by 0.5mm, and the heads are stamped 'A6' and 'FF' with the second 'F'inverted. I seem to remember that the 'A6' is indicative of strength - anybaody able to enlighten me further? Peter Chadwick Swindon 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.