What sewing notion is used to secure two pieces of fabric during assembly?

The use of pins as a sewing notion to secure two pieces of fabric during assembly is fundamental in sewing practice. Pins act as temporary fasteners that hold the fabric layers together, ensuring that they remain aligned while being sewn. This is particularly important for maintaining accuracy in seams and ensuring that the pieces fit together correctly, especially in complex patterns or when working with slippery fabrics.

Fusible interfacing serves a different purpose by providing stability and support to the fabric, but it does not hold pieces together during assembly. Thread is the actual medium used to stitch the layers together rather than secure them beforehand. A zipper is a fastening device used to close openings and is not used for aligning or holding fabric together during the initial assembly phase. Therefore, the primary function of pins in sewing is to aid in the assembly process by keeping fabrics in place until they are permanently joined by stitching.