Is It Safe to Mix and Match Fastener Nuts Occasionally?

Nuts and bolts of different standards may appear similar, and their performance is mostly redundant. It is often mistaken that the occasional mixing of nuts is okay. However, when selecting nuts and bolts, it should be ensured that the screw thread standards of the nuts and bolts are consistent.

Different countries and regions have different thread standards, such as Metric (Metric), United States (UNC/UNF), etc. Metric thread and American thread pitch, tooth Angle and other parameters are different, if arbitrarily mixed, will lead to poor screw fit, or even can not be tightened. This is because there are differences in the design of different standard threads, and their matching methods and stress conditions are also different.

In mechanical assembly, the mixed use of nuts may bring potential risks and should be carefully evaluated according to the specific scenario. As a professional nut manufacturer, Xinchi is happy to share the key considerations for nut mixing.

Potential problems with mixed nuts

Strength mismatch: If a high-grade bolt (such as 8.8) is matched with a low-grade nut (such as 4), it may cause thread shear failure.

Example: A class 8.8 bolt must be equipped with at least a class 8 nut, otherwise, the guaranteed load of the nut may be less than 70% of the tensile strength of the bolt.

Material compatibility: Mixing different materials (such as carbon steel and stainless steel) can cause electrochemical corrosion, especially in humid environments.

Data: When stainless steel is in contact with carbon steel, the corrosion rate can be increased by 3 to 5 times.

Size deviation: Nuts with different standards (such as ISO and ANSI) appear to have the same specifications, but differences in thread tolerances can lead to an uneven distribution of preload.

Limited scenarios for temporary mixing nuts

In case of emergency maintenance (no spare parts), the permissible condition is that the compliant parts must be replaced within 48 hours after mixing, and the risk control measure is to mark the mixing location and reduce the load by 20%.

If it is a low-load static connection, the allowable condition is the axial load < 30% of the bolt yield strength, and the risk control measure is to apply thread glue to compensate for the anti-loosening ability.

Strictly Prohibited Scenarios for mixingnuts

Bearing structure: Building steel structure, bridge bolt group, etc., must ensure that the nut and bolt grade, material is completely consistent.

Dynamic load environment: Mixed nuts in vibration scenarios, such as vehicle chassis and fan tower barrels, will significantly increase the risk of fatigue failure.

Special equipment: The flange connection of pressure vessels shall comply with ASME PCC-1 code, and it is prohibited to mix different materials or grades.

Specification suggestions for nut use

Marking management: Implement color or laser marking for different batches/types of nuts (e.g., 8.8 with blue, 10.9 with yellow).

Inventory control: FIFO (first in first out) principle is adopted to avoid confusion between new and old standard parts.

Inspection process: The GO/NOGO gauge is introduced to detect 100% thread clearance of mixed suspected parts.

The mixed use of nuts must strictly follow the principle of “same strength, same material, same standard” and is only accepted in non-critical temporary scenarios. Mixing of important connection parts may lead to chain failure. It is recommended to monitor the preload consistency by torque-angle curve (if the deviation is greater than 15%, it needs to be replaced).

XINCHI is a trustworthy fastener company, especially in furniture nuts. We have a factory,  founded in 2007. We are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  XINCHI can offer a wide range of high-quality fasteners, including nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. Our experienced and expert service team will reply to you as soon as possible.