Okay, this will be the first of a series-- I have a bunch of tools that I have absolutely no idea how to even begin to identify. For some this little quiz may be easy however, due to the fact that I am only familiar with tools that are still sold in stores (slowly getting better though, I figured out how to work a thumb planer earlier this week), this is quite a challenge in my book. This particularly sweet hunk of metal has a screw in the top and the bottom has some sort of threads and is hollow. Hard to tell from the photo but the tabs on the inside are pointed toward the back. The numbers embossed on it are hard to read as you can tell from the photo. Thanks in advance, and good luck!!