No matter what you're piecing you need a pin that's thin, sharp and heat resistant. There are the ones I always reach for. 

These long pins can hold together many layers of fabric. The flat head is convenient for machine stitching and you can lay a ruler on top of them without dealing with a bump. They are heat-resistant but don't put the iron directly on them. Size is .55mm x 50mm. (almost 2" long)

$ 3.95