These models are equipped with n hard steel pins (n = 1...3 pcs), which increases the friction between the workpiece and the jaw.
Clamps with code ending on Gn (e.g. DK2-VT-G2) contain n pieces of grip pins in both jaws. In clamps with code xK2-VT-RGn one jaw is serrated and hardened.
Clamp DK2-VT-RG3 (D-size with 3 grip pins in one jaw) is shown in the photo below.