The Singer Merritt 4525 sewing machine features a thread tension dial to help you easily adjust tension as needed. To ensure a proper and secure stitch, it is important to set the correct tension -- you want the needle and bobbin threads tightly locked between the two layers of fabric. Your fabric will pucker and bunch if the thread tension is too tight, causing unsightly seams. If the thread tension is too loose, loops will appear and weaken the seam.
Thread your Singer 4525 sewing machine with the thread you intend to use.
Use a scrap piece of fabric and stitch a sample. Examine it to determine whether the tension is too tight or too loose.
Increase tension by turning the thread tension dial to a higher number -- this eliminates any loops in the seam caused by a loose stitch. Decrease tension by turning the thread tension dial to a lower number -- this will keep your fabric from puckering.