Rambosky's right. Plus, it's very easy to get it off center. You need someone else to blaim if that happens.
The Threads on the beads are either 6-48 or 3-56. These are not standard thread sizes, so you would have to pay for the tap, drill bit and shipping.
Just pay the starving ole gunsmith the $20 he's gonna charge and be done with it.
Lee
The Arms Room
(another starving - but not so old - gunsmith)