I change my needle with every quilt. I use a size 18 with Permacore thread and a size 16 with Glide thread. These are the only 2 threads I use, therefore the only 2 sizes of needles I use. Recently when doing a batik quilt (all batiks front & back), I had to change the needle halfway through because it started shredding the Permacore thread. Needles are such a small expense as compared to everything else to do with quilting that I don't mind changing them often. I have a Gammill.