Pins are used to hold fabric layers together before sewing. There are several types available, but for quilting, long, thin straight pins are best. They don't leave a large hole and are easier to put in and out of fabric.
No. 1 or 1" non-corrosive safety pins are used to hold fabric layers together for machine quilting or when pinning many appliqué motifs on a project.
All pins should be non-corrosive and thin enough for use on appropriate fabrics. If your pins are not rustproof, they may leave stains on your projects if left pinned for long periods of time, especially during humid times of the year.