 A typical jig borer has a work table of around 400 x 200 mm, (16 x 8 inch) which can be moved using large handwheels (with micrometer-style readouts and verniers) on particularly carefully made shafts with a strong degree of gearing; this allows positions to be set on the two axes to an accuracy of 0.0001 inch (2.5 micron).It is generally used to enlarge to a precise size smaller holes drilled with less accurate machinery in approximately the correct place (i.e., with the small hole strictly within the area to be bored out for the large hole).Jig borers are limited to working materials that are still soft enough to be bored.