Tool for measuring roundness of inner diameter of large-diameter circular pipe orifice

The utility model discloses a tool for measuring the roundness of the inner diameter of a large-diameter circular pipe orifice, which comprises a dial indicator rod, a dial indicator clamp and a dial indicator, the dial indicator clamp comprises a clamping part and a locking part, the clamping part is provided with a rod groove penetrating from one end of the clamping part to the other end of the clamping part, and the locking part is provided with a locking part. The meter rod groove extends to one side face of the clamping part and divides one side of the clamping part into an upper end part and a lower end part, the clamping part is further provided with a first locking hole and a second locking hole, the first locking hole penetrates through the upper end part, the second locking hole penetrates through the lower end part, the inner surface of the first locking hole and the inner surface of the second locking hole are each provided with an inner thread, and the inner threads are matched with the inner thr