Material pair

Metal to Wood

Best bet

Waterproof, and grips both porous wood and smooth metal while filling small gaps.

Preparation

Prep each side differently

Scuff the metal with sandpaper and wipe off any oil or grease.

Sand to fresh fibers and brush off the dust.

Conditions

For a rigid, high-strength joint (furniture rails, brackets), switch to 2-part epoxy. Stay with polyurethane if the wood will move with humidity.