Sewing knitted fabric is different from sewing normal fabric. Jersey is a knitted fabric. If you destroy a thread in a knitted fabric, you get a run in the fabric.

With these needles especially for knitted fabrics you don't have this problem because this needle has a rounded tip that slips in between the threads instead of punching through threads. The threads stay intact, so no runs...

This pack contains 10 needles in the sizes 5 through 9.
(In hand sewing needles size 5 is heavier, and size 9 is finer)