Hi, Recently I found (at an ANTIQUES SALE) an old picture of a scientific instrument(optical) and I noticed a thread marked '20-Thury' . Do you know what is this type of thread ? Regards. PIerre pierre.courbouleix@xxxxxxxxxx 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.