Metric ISO 261
UNC/UNF ASME B1.1
BSP/G ISO 228
NPT ASME B1.20
Trapezoidal ISO TR
Cross-Reference
Engagement
Fastener Dims
ISO 261 Metric Threads — Coarse & Fine Series
Pitch diameter and minor diameter per ISO 724 · Tap drill = minor dia + 0.2–0.5mm allowance · Clearance holes per ISO 273 (fine/medium/coarse)
ASME B1.1 Unified National Threads — UNC & UNF
Tap drill sizes are standard drill letter/number/fraction designations · Clearance drill for standard fit · Thread depth = 0.6495 × pitch
Thread Engagement Length by Material
Minimum engagement length to develop full thread strength (based on tensile strength of the weaker material). d = nominal thread diameter.
Soft (plastics)
Medium (Al, brass)
Hard (steel, SS)
Helicoil / Thread Insert Benefit
Without insert (Al 6061)1.5–2.0× d
With Helicoil (Al 6061)1.0–1.5× d
Without insert (POM)2.0× d
With brass insert (POM)1.0× d
Engagement — Worked Example M8
Steel-in-steel8–12 mm
Steel-in-Al 606112–16 mm
Steel-in-ABS20–24 mm
Steel-in-Nylon PA620 mm min
ISO 228 / BS EN ISO 228 — BSP (G) Parallel Pipe Threads
Straight (parallel) threads for fluid-tight sealing with gasket/O-ring. BSPP = British Standard Parallel Pipe. Tap drill for female thread. Differs from BSPT (tapered).
ASME B1.20.1 — NPT / NPTF Tapered Pipe Threads
Taper = 1:16 (¾"/ft). NPT needs sealant (PTFE tape). NPTF (Dryseal) seals without sealant — tighter tolerances, same form. Tap drill for female thread at hand-tight reference plane.
ISO 2904 / DIN 103 — Metric Trapezoidal Threads (Tr)
29° flank angle (ISO metric). Used for lead screws, jacks, vises. High efficiency, self-locking with suitable pitch. ACME (29°) is the US equivalent.
Metric ↔ Imperial Thread Cross-Reference
Closest functional equivalent threads. These are NOT interchangeable — different pitch and form. Use only for reference when sourcing replacements or designing for dual-market products.
Fastener Reference Dimensions
ISO 4762 socket head cap screws · ISO 4017 hex bolts · ISO 4032 hex nuts · ISO 7089 plain washers. Dimensions for counterbore and clearance design.
Socket Head (ISO 4762)
Hex Bolt (ISO 4017)
Hex Nut (ISO 4032)
Washer (ISO 7089)
ISO 286-1 Fits & Tolerances
Common preferred fits for general engineering. Tolerance values in μm. Shaft system: H hole (zero-line) with varying shaft grade.
Tolerance Calculator
H7 Preferred Fits
H8 / H9 / H11 Fits
IT Grade Table
ISO 286 Tolerance Calculator
Enter nominal diameter and select hole+shaft grade. Calculates actual limits, fit type, and clearance/interference range per ISO 286-1.
Quick Presets
H7/g6 — Sliding
H7/h6 — Push
H7/k6 — Light press
H7/n6 — Transition
H7/p6 — Press fit
H7/s6 — Force fit
H9/d9 — Free running
H8/f7 — Close running
H11/c11 — Loose running
Nominal diameter (mm)
Hole grade
Shaft deviation
Shaft grade
Hole (H)
Shaft
Min clearance (+) / interference (−)
Max clearance (+) / interference (−)
Hole IT tolerance
Shaft IT tolerance
H7/g6 — Sliding / Locating Clearance
TypeClearance
UsePrecise sliding, locating
AssemblyHand push, no play
ExampleBearing in housing
H7/h6 — Push / Close Running
TypeClearance
UseAccurate location, no movement
AssemblyLight push
ExampleDowel pins, locating
H7/k6 — Transition Fit
TypeTransition
UseGood alignment, light press
AssemblyMallet or arbor press
ExampleGear hubs, pulleys
H7/n6 — Transition / Light Interference
TypeTransition
UsePermanent or semi-permanent
AssemblyPress fit or thermal
ExampleBushings, bearing races
H7/p6 — Press Fit (Interference)
TypeInterference
UsePermanent fit, torque transfer
AssemblyHydraulic or thermal
ExampleShaft couplings
H7/s6 — Force Fit (Heavy Interference)
TypeInterference
UseHeavy torque, no keys needed
AssemblyThermal expansion / press
ExampleWheel to axle
H7/g6 — Actual Tolerance Values (μm)
H7/k6 — Actual Tolerance Values (μm)
H7/p6 — Actual Tolerance Values (μm)
ISO 286 IT Grade Tolerances
Fundamental tolerance (IT) in μm for each grade and nominal diameter range. IT6 = typical precision machining, IT7 = standard, IT11 = rough.
ISO 1302 Surface Finish — Ra Values & Process Capability
Ra = arithmetic mean roughness. N-grade designations per ISO. Process capability Ra ranges are typical — actual results depend on machine condition, tooling, and material.
Application Guide
GD&T — ISO 1101 / ASME Y14.5 Geometric Characteristics
Symbols, datums, and tolerance zones for geometric dimensioning and tolerancing. ISO 1101 (metric) and ASME Y14.5-2018 (imperial) are largely harmonized.
Symbols & Zones
Datums & FCF
Typical Tolerances
Feature Control Frame (FCF) Reading
⊡Geometric characteristic symbol
∅0.05Tolerance value (∅ = cylindrical zone)
MMaterial condition modifier (MMC)
A | B | CDatum references (primary, secondary, tertiary)
Material Condition Modifiers
MMC ⓜMaximum Material Condition — bonus tol.
LMC ⓛLeast Material Condition
RFS (no symbol)Regardless of Feature Size (default)
Datum Reference Frame (3-2-1 Rule)
Primary datum (A)3 contact points — constrains 3 DOF
Secondary datum (B)2 contact points — constrains 2 DOF
Tertiary datum (C)1 contact point — constrains 1 DOF
Projection / Modifiers
PProjected tolerance zone
TTangent plane
CFContinuous feature
STStatistical tolerance (ASME)
General (Unspecified) Tolerances
Applied to dimensions without individual tolerance callouts on a drawing. Referenced in the title block. ISO 2768 is the European standard; ASME Y14.5 title block tolerances are the US equivalent.
ISO 2768 Linear
ISO 2768 Angular
ISO 2768 Geometric
ASME Title Block
f
Fine — precision machining
Use whenCNC, close tolerance
m
Medium — standard machining ★
Use whenGeneral CNC default
c
Coarse — casting, rough machined
Use whenCast/forged parts
v
Very Coarse — rough fabrication
Use whenWeldments, rough stock
Tolerance on angles not otherwise specified. Arm length = shorter of the two legs forming the angle.
ISO 2768-2 geometric tolerances (straightness, flatness, roundness, symmetry). Class H = fine, K = medium, L = coarse. Applied when no individual GD&T callout is given.
ASME Y14.5 Drawing Title Block Tolerances
Standard unspecified tolerances when using ASME drawings. Approximately equivalent to ISO 2768-m for most cases.
ISO 2768 ↔ ASME Equivalence
ISO 2768-f≈ ASME ±.010" / ±.005"
ISO 2768-m ★≈ ASME ±.030" (common)
ISO 2768-c≈ ASME ±.062"
ISO 2768-v≈ ASME ±1/32" fractional
Title Block Standard Callout
Metric drawingISO 2768-m K
Inch drawingTOLERANCES PER ASME Y14.5
Dual dimensionBoth standards apply
Manufacturing Process Capability — Achievable Tolerances
Typical achievable tolerances under normal production conditions. Tighter tolerances are possible with special tooling, setup, and inspection — at higher cost.
Machining
Sheet Metal
3D Printing
Casting & Moulding
Material Designation Cross-Reference
Equivalent designations across EN/ISO, ASTM/UNS, DIN, JIS, and AA standards. Properties are nominal — verify to current datasheets for critical applications.
Aluminium
Steel
Stainless Steel
Titanium
Copper Alloys
Engineering Plastics
Standard Stock Sizes & Profiles
Common off-the-shelf dimensions for aluminium, steel, and sheet material. Metric (ISO) primary — imperial equivalents where commonly stocked.
⚠ Stock availability varies by region and supplier. Confirm before designing around a specific section. Preferred sizes highlighted in red.
Round Bar / Rod
Sheet & Plate
Extrusions / Profiles
Tube & Pipe