These are some small machinists jacks I made for practice as much as anything else. The body is 1.0 inch hexagonal stainless steel 1.2 inches long, with a 3/8-16 thread in the upper half, and a matching 0.422 inch counter bore in the bottom. The bolts were made from a 0.625 hexagonal section of 12L14 steel 1.3 inches long with their heads rounded and polished. The round parts are stackable extensions 1.22 in diameter, 0.80 and 1.35 long (including knob), having a 0.422 bore in their bases and 0.400 knob on the top. There is nothing magical about any of these dimensions, they just fit the scrap bits I had on hand. In use the jacks can be adjusted with two wrenches-one on the body and one on the bolt head.
One thing I've discovered-I either need a tapping stand or a tapping head for the milling machine. Getting that thing straight is a lot of work.
All images and text Copyright Dale Austin, 1962-2008