The shanks should be long enough to protrude into the soil at least 4 inches. Mine have notch adjustments on 2" increments and extend about 6" below the bottom of the blade. You can get a bit more penetration by tilting the box blade forward if needed for just scarifying. If you plan to make your own, I would use at least 1/2 plate thickness, but personally I would not try to make them as they need to be tempered for hardness to avoid breaking. Too much temper and they break rather than bend and not enough hardness and they wont stand up and will constantly bend over.