The 4013TSW/4053TSW used the same double stack frame as your 6906. The 4056TSW used the same size frame, only in stainless.
The 4013/4053/4513TSW/4553TSW were single stack compacts with alloy frames.
The 4516/4556 were single stack compacts with stainless frames.
Obviously, any model number starting with 40 is a .40, and any starting with 45 is a .45.
A 3 on the end means alloy frame, a 6 means stainless.
A 1 near the end means a DA/SA action, while a 5 means DAO.
There will be a test at the end of the lesson.