Mounted a aluminum 1/2" x 1" bar stock to the bottom of the shrinker, with two 3/16" holes drilled 2.5" apart. 3/8" x 16 tpi threads. Sits nicely on the vise, which clamps down the aluminum bar stock.
Practice piece was some 2024 0.025 aluminum. Once formed, it is stiff! Pulling and tugging did get a split at the tooling marking. Solution is to lightly sand out all tooling marks when done.
Another way, to avoid marking, is using fine emery cloth between jaws and work piece and take a little longer.
www.toolmantech.com has them. I really should have bought the stretcher shrinker so both can be set up, but went with the 'combo package' that has a shrinker & frame, and stretcher. A friend had bought a Harbor Freight unit (yes initially cheaper), but the casting busted after a year. Lesson learned the Lancaster "Made in USA" castings hold up for 50 years, but never found a used one for sale.
