Feed dogs

A small spool that holds the lower thread supply, fitting into the bobbin case beneath the needle plate to form the underside of a lockstitch.

A metal or plastic holder that houses the bobbin and regulates lower-thread tension via an adjustable spring before the thread reaches the needle plate.

A spindle and motor mechanism on a sewing machine that winds thread evenly onto an empty bobbin, usually engaged by disengaging the main stitching mechanism.

The wheel at the right end of a sewing machine that manually raises and lowers the needle and can be turned to advance a single stitch.

A control that, when engaged, reverses the feed dog direction so the machine sews backward, commonly used to lock stitches at the start and end of a seam.