Nails can work loose over time— from floorboards, moldings, window trim, and stair-cases. You can put them back in with a nail set, a small, pen-shaped nail. Position the nail set on the exposed nail, tap the nail set with a hammer a couple of times, and the loose nail disappears from view. A medium nail set is suitable for small and medium nails. (Stanley nail set, $5 at .)