Selection and application of tolerance grades:
IT01: Used for particularly precise dimensional transfer datums, such as particularly precise standard blocks.
IT0: Used for particularly precise dimensional transfer datums and particularly important precision fit dimensions in aerospace. For example, particularly precise standardized blocks, individual particularly important dimensions of precision machine parts, proofreading gages for checking IT6 grade shaft gages.
IT1: Used for precision dimensional transfer reference, high-precision measuring tools are particularly important for individual precision fit dimensions. For example, high-precision standard gages, proofreading inspection IT7 to IT9 grade shaft gages proofreading gages, individual particularly important precision machine part dimensions.
IT2: Used for high precision measuring tools, especially important precision fit dimensions. For example, inspection of IT6 to IT7 level workpiece with the size of the manufacturing tolerance of the gauge, proofreading inspection of IT8 to IT11 level shaft with the checking of the gauge plug gauge, individual particularly important precision mechanical parts size.
IT3: used for precision measuring tools, small-sized parts of high-precision precision fit and and C-class rolling bearing with the shaft diameter and shell hole diameter. For example, inspection gages for workpieces of class IT8 to IT11 and calibration gages for inspection gages for shafts of class IT9 to IT13, machine tool spindles mated with the inner ring bores of particularly precise rolling bearings of class P4 (up to 100mm in diameter), the journals of precision and high-speed machinery, the housing bores mated with the outer rings of class P4 radial ball bearings, and the particularly precise individual bores of navigational instruments in the aeronautical and marine industries. Small size parts of the accuracy of the fit.
IT4: Used for precision measuring tools, high-precision precision fits and P4 and P5 rolling bearing fits for shaft diameters and housing bores. For example, inspection of IT9 to IT12 level workpiece with gages and proofreading IT12 to IT14 level shaft with gages for proofreading gages, with P4 level bearing holes (hole diameter >100mm) and with P5 level bearing holes with the machine tool spindle, precision machinery and high-speed mechanical journals, with P4 level bearing with the machine tool housing holes, diesel engine piston pins and piston pin seat aperture, high-precision (level 1 to 4) Gear reference hole or shaft diameter, aviation and marine industry with instruments of special precision aperture.
IT5: used to match the tolerance requirements are very small, shape tolerance requirements are very high under the regulations, this type of tolerance level can make the nature of the fit is relatively stable, equivalent to the old national standard in the highest precision, for machine tools, engines and instruments in the particularly important with the size of the general mechanical applications less. For example, the inspection of IT11 to IT14 level workpiece with the gauge and proofreading IT14 to IT15 level shaft with the gauge of the proofreading gauge, and P5 level rolling bearings with the machine tool box hole, and E level rolling bearing hole with the machine tool spindle, precision machinery and high-speed mechanical journals, the machine tool tailstock sleeve, high-precision indexing plate journal, indexing head spindle, precision screw reference journal, high-precision boring bushes, and so on the outside diameter; Engine in the spindle instrumentation in the precision holes in the fit, 5 precision gears of its holes and 5, 6 precision gears of the reference shaft.
IT6: with a high degree of uniformity of the surface requirements to ensure a high degree of fit, the use of stable and reliable, equivalent to the old national standard level 2 shafts and 1 level of precision holes, widely used in machinery, such as the important with the inspection of the IT12 to IT15 level of workpiece with the gauge and proofreading IT15 to IT16 level of shafts with the proofreading of the gauge; and the E-class bearings matching the shell holes and roller bearings matching the spindle of the machine tool. Roller bearings matched with the machine tool spindle journal, machine tool manufacturing of assembled bronze worm gears, wheel housing OD mounted gears, worm gears, couplings, pulleys, cam journals; machine tool screw bearing journals, rectangular spline centering diameter, rocker arm drilling machine columns, etc.; machine tool fixtures of the guide parts of the outer diameter of the dimensions of the fixtures, precision instruments in the precision shafts, aeronautical and marine instrumentation in the precision shafts, automation instrumentation, postal and telecom machines, the Watch in the particularly important shaft, the engine in the cylinder liner outer diameter, crankshaft main journal, piston pin, connecting rod bushings, connecting rods and axial tile outer diameter; 6 precision gear reference hole and 7, 8 precision gear reference journal, special precision such as 1 or 2 precision gears of the top circle diameter.
IT7: widely used in general machinery, the application of conditions similar to IT6, but the precision is slightly lower, equivalent to the old national standard of intermediate precision shafts or level 2 precision hole tolerance. For example, the inspection of IT14 to IT16 level workpiece with the gauge and proofreading IT16 level shaft with the proofreading gauge; machine tools in the assembled bronze worm wheel rim aperture, couplings, pulleys, cams and other apertures, machine tool chuck seat holes, rocker arm holes in the rocker arm of the drilling machine, the bearing holes in the lathe screws, machine tool chuck guides the inner hole, connecting rod holes in the engine, the piston holes, the hinging of the stud positioning holes; the important components of textile machinery, printing and dyeing machinery require Important parts in textile machinery, printing and dyeing machinery in the higher requirements of the parts, precision instruments with precision holes, electronic computers, electronic instruments, instruments in the important holes, automation instrumentation in the important holes, 7, 8 precision gear reference holes and 9, 10 precision gear reference shaft.
IT8: in mechanical manufacturing belongs to the medium precision, in instruments, meters and clocks manufacturing, due to the basic size is smaller, so belongs to the higher precision range, in agricultural machinery, textile machinery, printing and dyeing machinery, bicycles, sewing machines, medical equipment in a wide range of applications. For example, the inspection of IT16 level workpiece with the gauge, bearing housing bushes along the width direction of the size of the fit, the watch across the tooth axis, pawl dial wheel and other clamping plate with the radio instrumentation in the general fit.
IT9: application conditions are similar to IT8, but the precision is lower than IT8 when used, than the old national standard 4 precision tolerance value is slightly larger. For example, machine tools and holes in the outer diameter of the bushing, manipulation of parts and shaft, idle pulley and shaft, the shaft of the control system with the bearings, etc., textile machinery, printing and dyeing machinery in the general fit with the parts, the engine in the oil pump body holes, the inner hole of the valve guide, the flywheel and flywheel bushing fit, automated instrumentation in the general fit dimensions, the requirements of the watch parts in the size of the unnotched tolerance, the width of the key in the key coupling with the dimensions, the key in the key width fit. Fitting dimensions of moving parts in typewriters.
IT10: application conditions are similar to IT9, but the requirements of the precision is lower than IT9 when used, equivalent to the old national standard of precision tolerance level 5. For example, electronic instruments and meters in the bracket with the navigation instrument in the insulating bushing holes and converging ring bushing shaft, typewriters riveted parts with the size, the basic size of the watch is less than 18mm when the general requirements of the size of the unannotated tolerance, and greater than 18mm higher requirements of the size of the unannotated tolerance, the engine in the oil seal retaining ring holes with the crankshaft pulley with the hub with the size of the engine.
IT11: Widely used in the gap is large, and there are significant changes will not cause danger, can also be used to match the lower precision, assembly allows a larger gap, equivalent to the old national standard of precision tolerance of 6. For example, the flange stop and holes on the machine tool, slider and slip gear, groove, etc.; agricultural machinery, locomotive carcase parts and stamping parts, watch manufacturing in the unimportant parts, watch manufacturing tools and equipment in the unnotated tolerance size, textile machinery in the rougher activities with the printing and dyeing machinery in the requirements of the lower with the size of the grinder in the manufacture of threaded couplings and rough dynamic couplings, do not as Measurement of the reference for the gear top circle diameter tolerance, etc..
IT12: The requirement of fit accuracy is very low, there is a large gap after assembly, applicable to basically no fit requirements of the part, the requirement of higher limit deviation of the size of the unannotated tolerance, which is a little smaller than the old national standard of the precision tolerance of the 7 level. For example, non-matching dimensions and inter-process dimensions, engine separator rod, unnotched tolerance dimensions of process equipment in watch manufacturing, limit deviations of unnotched tolerance dimensions of metal processing in the computer industry, coupling of wrench holes and wrench holders in the machine tool manufacturing industry, and so on.
IT13: The application conditions are similar to those of IT12, but the tolerance values are slightly larger than those of the old national standard of grade 7 accuracy. For example, non-matching dimensions and inter-process dimensions, computers, typewriters in the cutting parts and circular holes, two holes in the center distance of the unannotated tolerance dimensions.
IT14: used for non-matching dimensions and dimensions not included in the dimensional chain, equivalent to the old national standard of precision tolerance of 8. For example, the limit deviation of unannotated tolerance dimensions of machined parts in machine tools, automobiles, tractors, metallurgical machinery, mining machinery, petrochemical industry, electric motors, electrical appliances, instruments and meters, aviation and navigation, medical equipment, clocks and watches, bicycles, sewing machines, paper making and textile machinery, and so on.
IT15: Used for non-matching dimensions and dimensions not included in the dimensional chain, equivalent to the old national standard of 9 precision tolerance. For example, stamping parts, wood mold casting parts, heavy machine tool manufacturing, when the basic size is greater than 3150mm when the limit deviation of the dimension of the unannotated tolerance.
IT16: used for non-matching dimensions, equivalent to the old national standard of precision tolerance of 10. For example, typewriters in the casting dimensions, radio manufacturing in the case dimensions, surgical instruments in the general dimensions, bending and extension of the processing of dimensions, textile machinery in the dimensions of the wood parts, plastic parts of the dimensions of the wood mold manufacturing and free forging dimensions.
IT17, IT18: for non-coincidental dimensions, equivalent to the old national standard of 11 or 12 precision tolerance for plastic molding dimensions, surgical instruments in the general shape of the size of the size of the cold and welding with the size of the tolerance.