A slam-shut safety device having a disc arrestor includes a valve body, a valve seat between an inlet and an outlet, and a reset pin shiftable between untripped and tripped positions. A valve disc support includes has a threaded stem and is operatively coupled to the reset pin. A valve disc fits on the stem of the support and shifts in response to movement of the valve disc support between an open position and a closed second position in which the valve disc is seated against the valve seat. A threaded nut is securable to the threaded portion of the stem of the valve disc support, and an arrestor spring is positioned on the stem of the valve disc support and is secured by the threaded nut. The arrestor spring is arranged to apply a biasing force to valve disc.