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In soft woods a pilot hole of about 50% core diameter will give
maximum holding power.

For woods of imtermediate density a pilot hole of 70% of core
diameter will give maximum holding power.

For hard woods such as oak a pilot hole of 90% of the core
diameter will give best holding power.

Then pilot holes of from 70 to 90% of core diameter will give
maximum holding effciency depending on the hardness of the
wood. The seasoning of the wood should also be considered.

Soap, or parafin may be used as a lubricant.

In choosing between two adequate screws use the smaller
diameter and the longer length when practicable.