Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
This is a good example. More often very difficult to see.
The 400 tended to get white marks and the 500/550 black ones. Those are really clear John. Can't mistake those.
If 550 conrods are the same as 500 ones I have a set going spare - just postage cost if it helps.