The utility model relates to the technical field of measurement, in particular to an inner
diameter measuring mechanism which comprises a base and a measuring
assembly. The measuring
assembly comprises two sliding blocks, a double-thread screw, two limiting frames, a positioning rod, a moving block, a pushing mechanism, a measuring rod, a connecting rod and a pointer. The base is provided with scale marks; during measurement, a
pipe cap is placed on the base, the positioning rod and the measuring rod are buckled, then the double-thread screw is rotated to drive the two sliding blocks to be close to each other, the two limiting frames are close to each other to slightly clamp the
pipe cap, the circle center of the
pipe cap, the circle center of the section of the positioning rod and the circle center of the section of the measuring rod are located on the same
vertical plane, and then the pushing mechanism is used for pushing the pipe cap to move. The movable block is pushed to drive the measuring rod to move rightwards until the positioning rod and the measuring rod abut against the left side and the right side of the inner wall of the pipe cap respectively, then
direct reading can be conducted according to the scale marks and the pointer, the reading is the inner
diameter of the pipe cap, calculation can be avoided, and the inner
diameter of the plastic pipe cap can be more conveniently and directly measured.