If you are looking at the Havahart trap #1025 for squirrel, may I suggest spending a little bit more for either the #1030 or the #1040.  All three models are good double door traps that are easy to use but, here is the difference:

The #1025 measures 18" x 5" x 5" with a door on each end. (Bottom trap in photo)
The #1030 measures 24" x 7" x 7" with a door on each end. (no photo)
The #1040 measures 30" x 7" x 7" with a door on each end. (Top trap in photo)
 
18" is just too short when you consider that when the squirrel has its nose at the bait tray, his whole tail is sticking out of the trap.  This doesn't allow the door to close, letting him escape. After that, he'll never go near it again.  The other two work beautifully. Of the three, I recommend the #1040.

Happy hunting!

10/21/06 Added the following:
10/11/06 Bought 1040 trap
10/15/06 caught 2 squirrels with it.
10/17/06 caught opossum      "
10/18/06 caught cat                "
10/18/06 caught squirrel         "
10/19/06 caught blue jay        "

10/01/07 set out traps
10/02/07 caught squirrel w/#1040 Havahart
10/03/07 caught squirrel w/#1040 Havahart

10/15/06 Bought 1030 trap for friend (he says 1040 is too big to use in the location he wants it for)
I guess size does matter.

Oh yes, if this was any help, check the yes box below.