IT0 1 is used for particularly accurate dimensional transfer benchmarks, such as particularly accurate standard gauge blocks.
IT0 is used for particularly precise dimension transfer datum and particularly important precision fit dimension in aerospace. For example, especially precise standard gauge blocks, the dimensions of individual particularly important precision mechanical parts, and check the proofreading gauges of IT6 shaft gauges.
IT 1 Precision dimension transfer datum and extremely important precision fit dimension for high-precision measuring tools. For example, high-precision standard gauges, check the calibration gauges of IT7-IT9 axis gauges, and the dimensions of individual particularly important precision mechanical parts.
IT2 is used for high-precision measuring tools, especially important precision fit dimensions. For example, check the dimension manufacturing tolerance of IT6-IT7 workpiece gauge, check the plug gauge of IT8-IT 1 1 axis gauge, and the dimensions of some particularly important precision mechanical parts.
IT3 is used for precision measuring tools, high-precision fitting of small-sized parts and shaft diameter and shell aperture matching with C-class rolling bearings. For example, check the gauge of IT8-IT 1 1 workpiece gauge, check the gauge of IT9-IT 13 axis gauge, the spindle of machine tool matched with the inner ring hole of P4 rolling bearing (diameter up to 100mm), the journal of precision machinery and high-speed machinery, and centripetal to P4.
IT4 is used for high-precision fitting and matching of precision measuring tools and P4 and P5 grade rolling bearings, including shaft diameter and shell aperture. For example, check the workpiece gauge from IT9 to IT 12 and the shaft gauge from IT 12 to IT 14, and compare with P4 bearing hole (diameter >); 100mm) and spindle of machine tool matched with P5 bearing hole, journal of precision machinery and high-speed machinery, casing hole of machine tool matched with P4 bearing, aperture of piston pin and piston pin seat of diesel engine, reference hole or shaft diameter of high-precision (1 to 4) gear, and special precision aperture of instruments used in aviation and navigation industry.
IT5 is used for procedures with small tolerance requirements and high shape tolerance requirements. This tolerance level can make the fit performance more stable, which is equivalent to the highest accuracy in the old national standard. It is used in machine tools, engines and instruments, and rarely used in general machinery. For example, check the workpiece gauge from IT 1 1 to IT 14, the shaft gauge from IT 14 to IT 15, the machine tool box hole matched with P5 rolling bearing, the machine tool spindle matched with E rolling bearing hole, the journal of precision machinery and high-speed machinery, and the machine tool tailstock. The matching of the precision hole of the spindle instrument, the hole of the 5-stage precision gear and the reference shaft of the 5-stage and 6-stage precision gear in the engine.
The mating surface of IT6 requires high uniformity, which can ensure quite high mating performance and is stable and reliable in use, which is equivalent to the second-class shaft and 1 precision hole in the old national standard. It is widely used in the important matching of machinery, such as checking the workpiece gauges from IT 12 to IT 15, and checking the calibration quantity of IT 16 shaft gauges. Shell holes matched with E-class bearings and spindle journals of machine tools matched with roller bearings, and journals of bronze worm gears, worm gears, couplings, pulleys and cams assembled in machine tool manufacturing; Machine tool lead screw support journal, rectangular spline centering diameter, radial drilling machine column, etc. The outer diameter of the guide part of the machine tool fixture, the precision shaft in precision instruments, the precision shaft in aviation and navigation instruments, the particularly important shaft in automation instruments, post and telecommunications machinery, clocks and watches, the outer diameter of the cylinder liner in the engine, the outer diameter of the crankshaft main journal, the piston pin, connecting rod bushing, connecting rod and bearing bush; The reference hole of the 6-level precision gear and the reference journal of the 7-level and 8-level precision gear are particularly precise, such as 1 or the top circle diameter of the 2-level precision gear.
IT7 is widely used in general machinery, and its operating conditions are similar to IT6, but its accuracy is slightly lower, which is equivalent to the tolerance of intermediate precision shaft or secondary precision hole in the old national standard. For example, check the workpiece consumption gauge from IT 14 to IT 16, and check the shaft consumption gauge from IT 16; The machine tool is equipped with bronze worm wheel rim hole, coupling hole, pulley hole, cam hole, etc. , seat hole of machine tool chuck, rocker hole of radial drilling machine, bearing hole of lathe screw, inner hole of guide rail of machine tool chuck, connecting rod hole and piston hole in engine, positioning hole of hinge stud; Important parts in textile machinery, parts with higher requirements in printing and dyeing machinery, inner holes with precise fit in precision instruments, important inner holes in electronic computers and instruments, important inner holes in automatic instruments, reference holes of 7 and 8 grade precision gears, and reference shafts of 9 and 10 grade precision gears.
IT8 belongs to the medium precision in mechanical manufacturing, and belongs to the high precision range in the manufacture of instruments, meters and clocks because of its small basic size. Widely used in agricultural machinery, textile machinery, printing and dyeing machinery, bicycles, sewing machines, medical equipment and so on. For example, check the IT 16 level workpiece dosage gauge, the dimensional fit of the bearing seat bushing along the width direction, and the general fit of the watch mid-span gear shaft, pawl wheel and splint in radio instruments.
The application condition of IT9 is similar to that of IT8, but its accuracy is lower than that of IT8, and slightly higher than the tolerance value of grade 4 accuracy in the old national standard. For example, the outer diameter and hole of shaft sleeve in machine tool, control part and shaft, idler wheel and shaft, shaft and bearing of control system, etc. General mating parts in textile machinery and printing and dyeing machinery, inner hole of oil pump in engine, mating of flywheel and flywheel sleeve, general mating dimensions in automatic instruments, tolerance-free dimensions of parts with higher requirements in watches, mating dimensions of key width in single key connection, and mating dimensions of moving parts in typewriters.
The application conditions of IT 10 are similar to those of IT9, but the required accuracy is lower than that of IT9, which is equivalent to the five-level accuracy tolerance of the old national standard. For example, the matching of brackets in electronic instruments and meters, the matching size of insulating bushing holes and bus ring bushing shafts in navigation instruments, riveted parts in typewriters, the size without general tolerance when the basic size of watches is less than 18 mm, the size with larger tolerance when it is greater than 18 mm, and the matching size of oil seal retaining ring holes and crankshaft hub in engines.
IT 1 1 is widely used in places with large clearance and no danger due to significant changes. It can also be used in situations with low matching precision and large clearance after assembly, which is equivalent to the 6-level precision tolerance of the old national standard. For example, flange stops and holes, sliders and sliding gears, grooves, etc. on machine tools. Agricultural machinery, motorcycle trunk parts and stamping parts, unimportant parts in clock manufacturing, dimensions without tolerance in tools and equipment used in clock manufacturing, rough fit in textile machinery, lower fit size required in printing and dyeing machinery, threaded connection and rough connection in grinding machine manufacturing, tolerance of gear top circle diameter not used as measurement reference, etc.
IT 12 has very low requirements for fitting accuracy, and there is a big gap after assembly. It is suitable for parts that basically have no matching requirements, and the size limit deviation without tolerance requirements is higher, which is slightly smaller than the 7-level precision tolerance of the old national standard. For example, mismatch size and inter-process size, engine release lever, unmarked tolerance size of process equipment in watch manufacturing, limit deviation of unmarked tolerance size in metal processing in computer industry, connection of wrench hole and wrench seat in machine tool manufacturing, etc.
The application conditions of IT 13 are similar to those of IT 12, but slightly larger than the tolerance value of the old national standard's grade 7 precision. For example, non-matching dimensions and inter-process dimensions, machining parts and disk holes in computers and typewriters, and the center distance between the two holes is not marked with tolerance dimensions.
IT 14 is used for mismatched dimensions and dimensions not included in the dimension chain, which is equivalent to the 8-level precision tolerance of the old national standard. Such as machine tools, automobiles, tractors, metallurgical machinery, mining machinery, petrochemicals, motors, electrical appliances, instruments, aviation and navigation, medical instruments, clocks, bicycles, sewing machines, paper making, textile machinery and other mechanical parts, the limit deviation of the tolerance size is not indicated.
IT 15 is used for mismatched dimensions and dimensions not included in the dimension chain, which is equivalent to the 9-level precision tolerance of the old national standard. For example, stamping parts, wooden die castings, heavy machine tool manufacturing, when the basic size is greater than 3 150 mm, the tolerance-free size limit deviation is not indicated.
IT 16 is used for non-matching dimensions, which is equivalent to the precision tolerance of 10 in the old national standard. For example, the dimensions of castings in typewriters, the external dimensions of boxes in radio manufacturing, the general external dimensions in surgical instruments, the dimensions of bending and stretching, the dimensions of wooden parts in textile machinery, the dimensions of plastic parts, the dimensions of wooden mold manufacturing and free forging.
IT 17 IT 18 is used for non-matching dimensions, which is equivalent to the tolerance 1 1 or 12 in the old national standard. It is used for the tolerance of plastic molding dimensions, the general external dimensions of surgical instruments and the dimensions of cold working and welding.