These target systems are awesome!
They work with standard medium duty T POSTs, find them at your local hardware store for a couple dollars. Essentially this is going to sit on a T POST after you put it together. Assembly takes 2 minutes. It is a large single piece of AR500. It bolts to a T POST bracket that we have designed with a 1/4" AR500 front plate for excellent bracket protection. You will bolt it to the T POST bracket with grade 8 bolts, 5/8". They are monsters, but work great. Simply put the HD SS compression spring in between our custom bracket and AR500 plate. Then go beat the crud out of it.