Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
get yourself a thread gauge, probable a couple of quid, they are like a small feeler gauge ,the edges of each blade are like the edge of a saw , that edge when put against the original screw will either fit it or not when you find the one that does it says the size on it so then you can measure the original screw length as well and confidently order the right screwpete