Just picked up a set of the rack extensions on eBay and before I try my hand at "freehand" drilling, I was wondering whether anyone out there had the drilling guide tool that I could borrow, rent or buy?

 

looked at the instructions posted elsewhere in the forum, and it looks like one could make a guide if they knew the outside diameter of the guide.

You could get some aluminum round stock that diameter and then just center a 4mm hole right in the center of the stock.

Does this make sense?

 

The instructions say the hole saw is 12mm -- could this also be the diameter of the guide tool itself?