Keeping their tunnels at approximately one body length in diameter seemed to ensure that the ants could catch themselves when they slipped and allowed the creatures to continue to dig.

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One approach might be to say that in order to be considered a major planet, a body needs to be larger than a certain diameter.

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The brass-plated body has a 'real-feel' pen diameter of nine milimetres and is coated with quality soft-touch rubber.

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This finding raises the question: can a small diameter lead be sufficiently robust to perform reliably over years of biologic exposure and mechanical stress in the human body?

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