You don't (unless you manipulate the jig by adding a shim or spacer(s). The 1/4" is set slightly above center for 1/2" to about 3/4" stock, the 5/16"is about center and the 3/8" is slightly below center for the larger stock.
This kit is made in China
Dear Customer, Thank you for your interest. Unfortunately, homedepot.com does not offer shipping outside of the U.S. Sincerely, MIBRO Customer Care
Yes although the dowels will not be centered in the butt of the 2x4. This is generally designed for wood 1” thickness or less
Dear Customer, Thank you for your inquiry. The M6 threaded dowel barrel nut is usually 10mm in diameter and the closest dowel size in the jig is 3/8” which is slightly small (roughly 0.5mm). We do not believe that the barrel nut will fit into the hole. Hope this helps. Sincerely, MIBRO Customer Care