The Knifty Knitter Long loom set comes with 4 long looms and a Knifty Knitter hook.
The Knifty Knitter round loom set comes with 4 round looms and a Knifty Knitter hook.
This is for anyone that has a difficult time weaving the yarn around the Knifty Knitter loom pegs. The loom tool is very in expensive at less than $2.00. I have also seen people use straws cut as homemade weaving loom tools, but they are not quite as effective as the Knifty Knitter tool.
The loom clips are for adjusting the size of any standard long loom. For example, if you are wanting to knit baby booties on the smallest long loom in the set, you can do this by using a loom clip to reduce the width to about half it's normal size.
If you are interested in a loom specifically for making hats, this loom is the correct size for most adults.