restructuring tables and model relationships in order to use STI

Hey James! I'm going back to the garage app and want to implement some of the things I learned from you over the last couple of weeks. As a first step, I'm restructuring the models and databases. Planning to use STI for Users (with Customers and Employees inheriting from User) and for Repairs, with Invoices and Estimates inheriting from Repairs.
Slightly worried about this class name. I don't think it's a reserved word, but it could lead to some confusion. Something that means the same thing, is nice and short like this, but doesn't also clash with a word we use in rails every day. It's not vital, but I think this would lead to some very confusing conversations down the road. It's usually only at this early stage that you can make such small changes which make such a big difference to how easy it is to think about an app. Changing this out in a mature app, after half the contributors cracked it, could amount to a couple days work, depending on how this model had eventually been used/subclassed/emulated.