The problem is with the property selectedTools. You've made it of type List, but the only type Struts will allow in a multi-value input is String. Change the type to String and it should work.
Also, I think it's a bit odd to try and stuff so many values into the multibox value attribute. I'd suggest just using the id value, and then looking up the rest of the values in the Action class to which the form is submitted, either by doing a database call, or by looking up the value in a session-scoped List or HashMap.