A Rocker Arm Stud Girdle (aka valvetrain stabilizer) is a bar that links all the rocker arm studs together. It clamps over the polylocks on Stud Mount Rocker Arms
A Scorpion stud girdle distributes the load across all the studs. This adds strength and rigidity to the valvetrain.
Stud girdles are used in race engines with aggressive camshafts. The high lift and stiff valve springs can cause the rocker studs to flex. this will result in a loss of power at high rpm. On a dyno, it will look like power going up and down in waves.
If the flexing studs are not addressed, they can bend and/or break. This will obviously cause engine damage.
Scorpion Stud Girdles are a cost-effective alternative to Scorpion Shaft Mount Rocker Arms. However, they are not foolproof. They will add stability and reliability. But, they make valve adjustments more difficult. You may also need taller valve covers for clearance of the stud girdle.