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I would not touch this with a 20-foot pole or with a 20-feet pole,

which of those two is correct. I know that 20 feet is the length of the pole
Comments 
Hi,

I would not touch this with a 20-foot pole or with a 20-feet pole,

which of those two is correct. I know that 20 feet is the length of the pole

The traditional expression is I would not touch this with a 10-foot pole.

Say 'foot' rather than 'feet' when the term is used adjectivally.

Best wishes, Clive