Why Do Machine Screws Loosen and How to Prevent It
By Mutual Screw & Supply | Published: 2026-10-23
Category: Tips & Care
Learn why machine screws loosen under vibration and how to prevent it with proper selection, installation, and locking methods.
Quick answer
Machine screws loosen primarily due to vibration, thermal cycling, or improper installation. Prevent loosening by selecting the right screw type, using locking methods like threadlocker or nylon patch, and ensuring proper torque.
Vibration is the main cause of loosening
When machine screws are used in applications with constant motion or vibration—such as machinery, enclosures, or panels—the repeated forces can cause the threads to back out over time. This is especially true for coarse threads like #10-24 UNC, which have fewer threads per inch and less resistance to rotational loosening.
Thermal expansion and contraction
Temperature changes cause materials to expand and contract. If the screw and the mating material have different coefficients of thermal expansion, the clamping force can reduce, allowing the screw to loosen. This is common in outdoor or industrial environments.
Improper installation torque
Under-tightening leaves the screw vulnerable to vibration; over-tightening can strip threads or damage the material. Always use a torque wrench or follow manufacturer recommendations for the screw size and material.
Diagnosis and prevention steps
- Symptom: Screw backs out or loses clamping force after a period of use.
- Likely cause: Vibration, thermal cycling, or under/over-tightening.
- Corrective action: Apply a threadlocking adhesive (e.g., Loctite) or use screws with a pre-applied nylon patch. Retighten to the correct torque specification. If threads are damaged, replace the screw before applying any locking method.
- When to stop or choose another option: If the application experiences high vibration or safety-critical loads, consider using a locking fastener like a nylon patch screw or a mechanical lock washer instead of relying on threadlocker alone. For permanent installations, evaluate if a thread-forming screw or a different fastener type is more suitable.
Product facts
- #10-24 X 3" Machine Screws | Round Head Slotted Drive | Plain Steel (400 / Pkg.): Plain (uncoated) steel machine screw for general-purpose, indoor fastening where corrosion resistance is not required. For indoor applications without high vibration, the #10-24 slotted round head screw is a cost-effective choice, but it may need additional locking methods if vibration is present.
#10-24 X 3" Machine Screws | Round Head Slotted Drive | Plain Steel (400 / Pkg.) - #2-56 X 1/4" Machine Screws | Pan Head Phillips Drive | Steel Black Oxide (1000 / Pkg.): These #2-56 x 1/4" machine screws are manufactured from Steel with a black oxide finish, featuring a phillips drive and a pan head. The black oxide finish provides mild corrosion resistance and the Phillips drive allows for better torque transfer, reducing the chance of cam-out during installation.
#2-56 X 1/4" Machine Screws | Pan Head Phillips Drive | Steel Black Oxide (1000 / Pkg.)
