Which stitch is commonly used for sewing down a hem?

The blind hem stitch is specifically designed for finishing hems discreetly, making it an ideal choice for this purpose. This stitch allows the fabric to appear almost seamless from the front, as it only catches a few threads of the main fabric, keeping the hem less visible. This is particularly useful in sewing garments where maintaining a clean and polished look is essential.

In contrast, while a zigzag stitch can provide some stretch and is often used for finishing raw edges, it does not create the same invisible effect as the blind hem stitch when sewing down hems. A straight stitch is fundamental for general sewing but would be visible on the front side of the hem, defeating the purpose of a hidden finish. The overlock stitch is mainly intended for finishing edges and preventing fraying rather than providing a discreet hem, making it less suitable for this particular application.