I had a collection of the small inexpensive seam rippers and when they got dull, I tossed them in the trash. When all were gone, I invested in a Clover brand seam ripper. I don't recall the number but it has been in use about two years and is just as sharp now as when I bought it and trust me, I have used is a lot.
. When the time comes to replace, I would go Clover again. The four dollars I spent was a good investment. Long lasting and minimal frustration.
