I have the Adler 205-370 and am having problems with the top thread fraying. I have 277 top thread, brand new 25 needle (does not have a burr) and 200 shim. Bobbin has 207 thread. Checked the timing and the shuttle hook is just barely behind the needle. I worry about loosening the 2 round tightening bolts underneath - the screws are so very tight and once when I did try and tighten them I could not get them tight again without shifting the hook every time - had to call a repairman to tighten them and keep/get the hook to stay where it needed to be. Is there a sequence of which bolt underneath to undo first? Or how to position/fix the (axel?) underneath in a way so the hook won't shift off this careful placement so easily? It's hard to keep looking up from underneath the machine to the side bobbin case area. I assume the hook not being forward enough - to the front end of the needle is the cause of fraying top thread. There IS some PLAY in the shuttle hook movement, i.e. when everything is tightened you can jigger it back and forth a tiny bit, about half the width of the needle as you view the needle from the long groove side. Should I aim for the hook to be at the center of the needle, the long groove side - when the hook is sitting still ... though you could jigger it forward a bit? Thanks in advance. AB