Re: Found in the woods - Metal Tube with with screw on end
I would recommend taking it to the local sherfiff's department and let their EOD guys look at it. I've seen all kinds of ordnance over the years and I've not seen anything like that, but that doesn't mean it still doesn't have explosive material in it. As mentioned before, seismic charge, maybe an old style blasting cap, maybe a home made blasting cap, detonator, etc.
If you are determined to open it yourself, make sure you are grounded and you ground the case of the device to prevent static charge build-up. Just in case.
IMO, the EOD guys are your safest bet. Most likely it is harmless, but why take the chance?