This kit is perfect for anyone who doesnt already own a HoopMaster System and wants everything needed to start using a 5.5 Mighty Hoop right away. The HoopMaster System makes placing Mighty Hoops on garments fast, easy, and consistently accurate. While the Mighty Hoops can be used on their own, the HoopMaster greatly simplifies the process and helps ensure professional results every time. This is the most popular starter kit for first-time HoopMaster buyers. The inside dimension of this hoop is 5 5/16 (5.30, or 135mm), actual sewing area depends on brand of machine between to 4 5/16 to 4 13/16 (110 to 122mm).