I made this metal concrete mold out of C channels and a Bridgeport Mill. All of the parts were laid out so each piece could be interchangeable. All of the mounting points were drilled out with a #7 drill bit and then tapped for 1/4-20 bolts. Wedge washers were used so as to not bend the bolts when tightening them down. These molds are used to cast uniform freeze thaw specimens according to ASTM standards A few of the molds have spots to insert a thermocouple into it to record internal temperature.
It looks like the design has worked out well as they have been around now for many years.