Terminator,

I can't recall the size but yes, drill out the bottom hole until the thread end can JUST pass thru. Then it is held in place with a nylon locknut.

The pant should be "notched out" too to tightly fit over the outer hexshape.

The upper hole is for a screw to "lock" the pant in place and prevent it from rotating. (But if you notch out a nice little hex shape in the pant, it will help too..

See here: