A thread tapping device has a main seat, a rotating head, a handle rod, an adjustment rod, a pivot connector, and a pair of scrape blades. The main seat has a V-shaped groove, a bottom pivot hole, a through aperture, two connection bars, and an end block. The rotating head is disposed on the handle rod and inserted in the bottom pivot hole of the main seat. The adjustment rod has an upper lug and an outer threaded portion inserted in the rotating head. The pivot connector has a round aperture, a circular aperture, and a lower groove to receive the upper lug of the adjustment rod. Each scrape blade is disposed between the end block and one of the connection bars.