用于高精度测量内孔，精度达0.001-0.005mm。测量范围：6-12mm,11-20mm,20-40mm,40-100mm,100-125mm,125-150mm,150-175mm,175-200mm,200-225mm,225-250mm,250-275mm,275-300mm。6-100mm,又分为通孔三爪内径千分尺和盲孔三爪内径千分尺。