Query: ten-foot pole

[Cohen, Gerald Leonard]

A student has asked me about the expression "not to touch sth. with a
ten-foot pole."  Why is it a ten-foot pole and not, say, 9 feet long?

I didn't have an answer.  Would anyone perhaps know?  Were there any poles
actually known to be 10-feet long (used for a particular purpose) which
could have provided a rationale for the expression?

Gerald Cohen

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