Which of the following is NOT used to apply nail oil?

The use of nail oil typically involves application methods that ensure even and controlled distribution of the product, while preserving hygiene and preventing contamination. An eyedropper is specifically designed to dispense liquid in small amounts directly onto the nails, making it an effective tool for applying nail oil precisely where needed.

A cotton swab and a cotton-tipped wooden pusher also serve the purpose of applying nail oil, as they allow for a targeted application without excessive mess. The cotton swab can be used to apply oil around the cuticles and nails, while the wooden pusher can help to carefully apply oil in tight spaces.

In contrast, a nail brush is primarily used for cleaning nails rather than applying oil. Its bristles are designed for scrubbing and cleaning nail surfaces, not for the gentle or precise application of liquids like nail oil. Hence, it does not fit the context of applying nail oil, making it the correct choice to identify as NOT used for this purpose.