I use silk thread for appliqueing. It is very fine, and I don't think it is appropriate for what you want. However there is silk floss, perhaps that is what you had in mind. There is also silk ribbon, and it would be beautiful on a crazy quilt. There are a number of books out there with silk ribbon flowers, bugs etc. lThat would help you out. For the most part 4mm, 7mm, 1.8mm are the ones offered by Bucilla. There are more I would imagine! Anyway, get a book or take a class, it will give you a much better idea of what you will need. By the way there is also wired silk ribbon such as the kind that Elly Sienk(sorry I can't spell her name!), and these are to make large flowers. Not what you would use on a crazy quilt. Don't forget metalic floss, it would be beautiful.