IBM ThinkPad ThinkPad Mini Dock User Manual page 17

If you use the ThinkPad Mini Dock, and attach a mechanical lock, the release
button is not locked. To lock the release button, use the security lock key.
®
IBM does not offer a mechanical lock. You will need to purchase one
elsewhere. You are responsible for evaluating, selecting, and implementing any
locking device and security feature. IBM makes no comments, judgments, or
warranties about the function, quality, or performance of any locking device or
security features.
Attach a mechanical lock as follows:
The drawing is for the ThinkPad Port Replicator II.
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About the ThinkPad Port Replicator, the Port Replicator II, and the Mini Dock