Because the formula doesn't seem to work for standard bolts.

Examples - a 1/4 inch bolt takes a 7/16 wrench. The formula listed would tell you to use a 1/2 inch wrench.


A 3/8 bolt takes a 9/16 wrench, not a 3/4 inch wrench as you have listed. By the formula, a 3/8 bolt would need an 11/16 wrench, not exactly 3/4.

So much for free advice.

SteveM.

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