If printed at original size, the holes are made to fit #6 standard bolt and hexnut hardware. Have not tested it, but M4 parts should also fit. So far it seems to be very strong when printed with 100% fill.
Note: Your slicer may show a few errors regarding self intersections. Those are located where the stem meets the body. They are very minimal, and as you can see it prints just fine (ReplicatorG). If you have a full version of NetFabb, it can be fixed there. (I don't)