What reason does 8mm long screws slide thread have?

Sometimes, 8mm long screws will appear in the case of sliding thread, which is to use a spanner to twist there is no way to twist. Why is this?

The outside diameter of the 8mm long screws is too small. If the internal threads used in normal machinery and equipment are of normal size and can pass through the plug gauge, the small size of the external threads will cause the thread to slip.

Second, the strength of the screw. Because long screws are much longer than our usual screws. A screw of this length may bend if it is to be hardened. So some screw manufacturers in the production of this kind of screw will use the way of welding production, the same strength of the rod welded together. But this kind of screw that’s welded together, it’s a little bit weaker than the original one, and if it’s a little bit weaker, it can’t withstand the torque, and it slips. However, it is also possible that the material and process problems lead to the screw sliding thread.

Three, strength. Each screw has a different torque range, and if you twist the long screw beyond the specified load of the screw, you may slip the thread, or the screw may break.

Four, stop the regulation problem. 8mm long screws at the end of the gauge, can pass the gauge, but stop the gauge can not stop, will also occur sliding thread.