1. The holes of non-standard screws and nuts do not match.

Non-standard screws and nuts on machines that are subject to lateral loads and shear forces, such as driveshaft bolts and flywheel bolts, are transition-fitted to the bolt holes. The device should be robust and reliable and can withstand lateral forces. Some people don't pay attention to inspection during assembly and still install the unit when there is a large gap between the bolt and the bolt hole.

2. Non-standard screws and nuts should be thick but not thin.

Important joint bolts on machines, such as driveshafts and flyshafts, are usually finely threaded. Some people switch to coarse-toothed bolts when parts are lost in maintenance. Due to the larger inner diameter, smaller pitch and outer angle of fine-toothed bolts, high strength, good self-locking performance, and strong ability to withstand shock, vibration and AC loads; after replacing with coarse-toothed bolts, it is easy to loosen, fall off and crack, A mechanical accident occurs.

3. Non-standard screws and nuts have multiple washers.

In equipment, sometimes the assembled non-standard screws and nuts are too long, so someone installs many spring washers on one bolt. In this way, the tension spring washer is not uniformly stressed during the strengthening process, and some will crack, reducing the pre-tightening force of the bolt; or eccentric load will reduce the reliability of the bolt connection.

4. Washers for non-standard screws and nuts are too large.

Sometimes, due to lack of suitable gaskets, some people switch to larger ID gaskets. In this way, the contact area between the underside of the bolt head and the washer is small, the bearing force or locking force of the washer is reduced, and the bolt is easily loosened under the action of vibration and shock loads.

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