A Model F keyboard looks like this:
As you can see, it only has 10 function keys on the left side, and it has a rather bizarre layout. These do not need to be boltmodded, as they are held together with bent metal tabs, as shown below:
If you have a Model F, you can keep reading for curiousity. Otherwise, click here to return to the previous page.
A Model M keyboard looks similar to this:
This is an example of an IBM-made Model M. There are many variants of Model M keyboards, and I recommend you look at Wikipedia for further identification information.