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Straight answers to common questions about choosing, fitting and looking after M8-thread MIG contact tips.
M8 is the diameter of the thread that screws the tip into the torch. Contact tips come with several thread sizes, commonly M6, M8 and M10, and the thread must match the torch's tip holder.Larger tips are generally found on torches built for heavier current, but the thread size does not tell you a torch's rating. Check the torch's data plate and parts list for the correct tip, including its length and body diameter, as these differ between designs.
Choose the tip whose bore is stated for your wire diameter, which is printed on the wire spool. The tip is usually marked with its bore size as well.An oversized tip with a smaller wire causes arcing and speeds up wear. When you change wire size, change the tip, the drive rolls and the liner together, as each one is sized to the wire. A liner that is too big for the wire can cause the wire to tangle.
Look at the hole. The wire wears the bore into an oval shape, which is the first and most telling sign. You may also see an unsteady arc, difficult starts, wire that feeds in fits and starts, or wire welded into the tip.Change tips by their condition rather than a fixed schedule, and do not file or ream a worn one. On heavier work, wire travels through the tip in large amounts, so tips wear steadily and should be inspected often.
Hand-tighten the tip until it seats, then snug it with the proper tool. Avoid over-tightening, which can cause feeding issues and damage the threads.A loose tip overheats and wears out sooner, and blue or purple threads are a sign it has been running hot. If it keeps working loose, check the tip holder for damage, make sure you have the right thread and seat, and replace worn parts.