What Type / Size Bolt Holds In A Padlock Cylinder?
What Type / Size Bolt Holds In A Padlock Cylinder?
Most standard padlocks use a small retaining bolt to secure the cylinder inside the lock body. This bolt does not provide security on its own. Instead, it simply keeps the cylinder fixed in place so that the key mechanism aligns with the locking mechanism. When this bolt works loose, the cylinder can fall out, often resulting in the bolt being lost.
Typical Bolt Specification
In most padlock designs, the retaining bolt is a countersunk M4 bolt with a 5mm thread length. This is a common hardware size and is easy to source. The countersunk shape allows the bolt to sit flush within the padlock body, preventing interference with the internal mechanism.
Why Stainless Steel Is Recommended
Padlocks are often exposed to outdoor environments. A stainless steel bolt offers better corrosion resistance and reduces the chance of rust binding the bolt in place. Rusted bolts can cause the cylinder to jam or become difficult to remove for maintenance.
Thread Locking Compounds
Manufacturers usually apply a thread-locking compound such as Loctite to prevent the bolt gradually backing out during use. If you replace the bolt, apply a small amount of medium-strength thread-locker.
This ensures the bolt remains secure without making future removal impossible.
Measuring And Replacing The Bolt
If you are unsure whether your padlock uses the standard size, measure the internal bolt hole with a simple M4 test screw. If it threads smoothly without force or slack, the size is correct. Replacement bolts are sold in small packs at most DIY stores or online hardware suppliers.
When The Size May Differ
Some specialist, high-security, or older padlocks may use different bolt lengths or thread specifications.
In these cases, contacting the manufacturer or checking a technical datasheet is the most reliable approach.
Key Points To Remember
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Most padlocks use a countersunk M4 bolt, 5mm thread length
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The bolt retains the cylinder and is not a primary security feature
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Choose stainless steel to prevent corrosion
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Use a small amount of thread-lock to prevent loosening over time
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Some specialist padlocks may vary; confirm if unsure
In Practice
Replacing this bolt is quick and inexpensive. Once replaced, ensure the cylinder sits flush and the bolt is tightened securely but not overtightened. A proper fit will keep the padlock operating smoothly for long-term use.