Technical Reference
ISO fits & tolerances
Standard: ISO 286-2 · hole and shaft tolerance tables
Look up a hole or shaft independently. Use the fit visualiser when you want to compare them.
Position
Grade
Position
Grade
Standard, coverage, and source
ISO 286-1 defines the system; ISO 286-2 provides the tolerance tables. DIN 7160 (shafts) and DIN 7161 (holes) are earlier references superseded by DIN ISO 286-2. They are standard designations, while H7 and g6 are tolerance classes within the system.
Numerical tables from the supplied MechTab 3.0.1 reference cover 1–500 mm and all its available hole and shaft classes, including H1–H18 and h1–h18. Grades vary by tolerance position. Greyed-out choices have no entry for the current diameter. Upper size-band boundaries are included; values are not extrapolated. These legacy reference tables are not a certified implementation of a particular ISO edition.
WDS ISO tolerance tables ↗Threads
Standards: ISO 261 · pitches; ISO 724 · basic dimensions
Choose metric coarse or fine threads, or American unified inch threads.
The diameter-minus-pitch drill value is a starting estimate for cutting taps, not forming taps. Choose an available drill within the tap maker’s recommended range.
Standards, geometry, and sources
Metric pitches: ISO 261. Basic dimensions: ISO 724. Thread tolerance classes are covered by ISO 965-1; this tool shows basic geometry rather than class-specific limits. American UNC/UNF threads use ASME B1.1; 2A/2B tolerance limits are not calculated here. Unified threads are straight 60° fastening threads, not NPT pipe threads.
ISO 724 ↗ · ASME B1.1 ↗ · UNC / UNF pitch chart ↗
Basic 60° metric thread geometry: pitch diameter d − 0.649519P; internal minor diameter D − 1.082532P. These are basic dimensions, not tolerance limits. Tensile stress area: π/4 × (d − 0.9382P)².
Guhring tap sizes and drill ranges ↗Surface roughness
Translate an Ra value between micrometres and microinches, or look up a legacy drawing grade.
Ra and Rz describe different things
Ra is the arithmetic average of absolute profile deviations. Rz describes profile height according to the specified standard. There is no universal exact conversion between them.
N grades are legacy shorthand. For inspection, follow the drawing’s parameter, standard, filtering, and measurement requirements.
Measurement reference
Mitutoyo surface measurement guide ↗Wrench sizes
ISO reference: ISO 272 · hexagon widths across flats
Bolt diameter and wrench size are different. Select the head standard to find the across-flats size.
For standard hex heads. Socket-head, flange, and heavy-hex fasteners can differ; check the actual fastener specification.
Compare standards
Across-flats sizes depend on the fastener product standard as well as the thread size. ISO 272 covers hexagon widths across flats; the ISO, DIN, and JIS columns below are the published bolt-head comparisons from Bolt Depot, not a full fastener specification.
ISO 272 ↗| Bolt | ISO | DIN | JIS |
|---|
Tightening torque
Estimate torque from a specified target preload and nut factor.
Use the approved joint specification for assembly. Nut factor depends on the fastener, coating, lubrication, and bearing surfaces. This estimate does not check bolt strength, joint capacity, or tightening scatter.
Formula and assumptions
T = K × F × d, with preload F in newtons and diameter d in metres. K is a nut factor, not the thread friction coefficient. Strength class alone does not define a torque specification.
Bossard preload and tightening guidance ↗