[Features] Singer Apollo Bobbin Case For Singer Top Drop In Bobbin Sewing Machines. Singer Bobbin Case Holder #421325 Fits Singer Models The bobbin case is the part of the sewing machine that the bobbin is inserted into, that holds the tension of the bobbin thread. Tension is adjustable via a screw on the side of the bobbin case. Be sure to use the bobbins that are specifically designed to work with this bobbin case, as other bobbins will cause skipped stitches and can cause bigger problems for your sewing machine. [product information] product name:Sewing machine bobbin case color:black Use: Sewing equipment size:40*34*12mm Packing list (you can get after purchasing one item): Sewing machine bobbin case x 1 Please understand: 1. Due to the long shipping time, the item may be damaged during the shipping process, if the item is damaged, please leave us a message through the official website immediately before posting comments, and I will solve the problem for you. 2. Due to manual measurement, the size may have an error of 1-3cm. 3. Colors may vary from monitor to monitor.