What Is a Trapezoidal Thread?
Trapezoidal threads (designated Tr) are a power transmission thread form defined by DIN 103 (Germany) and ISO 2903 (international). They are characterised by a 30° included angle — 15° on each flank — and a flat crest and root profile. This form provides high load-carrying capacity, good self-locking properties, and is easy to manufacture with standard tooling.
Trapezoidal threads are the European standard for lead screws and power transmission applications — equivalent in purpose to ACME threads in North America, but with a different angle and dimensional system. They are used throughout European machine tool manufacturing, as well as in Asian, Middle Eastern, and global industrial markets that follow European standards.
Primary Applications
Trapezoidal vs ACME vs Metric Thread — Key Differences
Trapezoidal (Tr) and ACME threads are both power transmission threads, but they use different angles and dimensional systems and are not interchangeable. Metric threads are fastening threads — different purpose entirely. Using the wrong gauge type will produce incorrect inspection results.
| Thread Form | Angle | Standard | Designation | Primary Region | Interchangeable? |
|---|---|---|---|---|---|
| Trapezoidal (Tr) | 30° | DIN 103 / ISO 2903 | Tr 20×4 | Europe · Asia · Global | No |
| ACME | 29° | ASME B1.5 | 1″-5 ACME-2G | USA · Canada | No |
| Metric ISO (M) | 60° | ISO 261 / DIN 13 | M12×1.75-6H | Global (fastening) | No |
Tr and ACME are NOT interchangeable. The 1° difference in thread angle (30° vs 29°) means that Tr and ACME gauges will not produce correct inspection results when used on the other thread form. Always confirm whether your drawing specifies Tr (DIN 103 / ISO 2903) or ACME (ASME B1.5) before ordering gauges. For ACME gauges, see our ACME Thread Gauge Guide.
Trapezoidal Thread Designation — How to Read Tr Callouts
Trapezoidal thread callouts follow a specific format. Understanding the callout is essential for ordering the correct gauge.
| Callout Example | Meaning | Gauge Needed |
|---|---|---|
| Tr 16×4 — 7H | Internal Tr thread, 16mm diameter, 4mm pitch, class 7H | Tr 16×4 7H Thread Plug Gauge |
| Tr 20×4 — 7e | External Tr thread, 20mm diameter, 4mm pitch, class 7e | Tr 20×4 7e Thread Ring Gauge |
| Tr 32×6 — 7H | Internal Tr thread, 32mm diameter, 6mm pitch, class 7H | Tr 32×6 7H Thread Plug Gauge |
| Tr 40×7 — 8H | Internal Tr thread, 40mm diameter, 7mm pitch, class 8H (loose) | Tr 40×7 8H Thread Plug Gauge |
| Tr 52×8 — 7e | External Tr thread, 52mm diameter, 8mm pitch, class 7e | Tr 52×8 7e Thread Ring Gauge |
Trapezoidal Thread Size Chart — Tr8 to Tr100
Standard: DIN 103 / ISO 2903. All dimensions in millimetres. Thread depth = 0.5 × pitch. Default tolerance class: 7H (internal) / 7e (external).
| Designation | Pitch mm | Major Ø mm | Pitch Ø mm | Minor Ø mm | Thread Depth mm | Gauge |
|---|---|---|---|---|---|---|
| Tr 8×1.5 | 1.5 | 8.000 | 7.250 | 6.500 | 0.750 | Quote |
| Tr 10×2 | 2.0 | 10.000 | 9.000 | 8.000 | 1.000 | Quote |
| Tr 12×3 | 3.0 | 12.000 | 10.500 | 9.000 | 1.500 | Quote |
| Tr 14×3 | 3.0 | 14.000 | 12.500 | 11.000 | 1.500 | Quote |
| Tr 16×4 | 4.0 | 16.000 | 14.000 | 12.000 | 2.000 | Quote |
| Tr 18×4 | 4.0 | 18.000 | 16.000 | 14.000 | 2.000 | Quote |
| Tr 20×4 | 4.0 | 20.000 | 18.000 | 16.000 | 2.000 | Quote |
| Tr 22×5 | 5.0 | 22.000 | 19.500 | 17.000 | 2.500 | Quote |
| Tr 24×5 | 5.0 | 24.000 | 21.500 | 19.000 | 2.500 | Quote |
| Tr 26×5 | 5.0 | 26.000 | 23.500 | 21.000 | 2.500 | Quote |
| Tr 28×5 | 5.0 | 28.000 | 25.500 | 23.000 | 2.500 | Quote |
| Tr 30×6 | 6.0 | 30.000 | 27.000 | 24.000 | 3.000 | Quote |
| Tr 32×6 | 6.0 | 32.000 | 29.000 | 26.000 | 3.000 | Quote |
| Tr 36×6 | 6.0 | 36.000 | 33.000 | 30.000 | 3.000 | Quote |
| Tr 40×7 | 7.0 | 40.000 | 36.500 | 33.000 | 3.500 | Quote |
| Tr 44×7 | 7.0 | 44.000 | 40.500 | 37.000 | 3.500 | Quote |
| Tr 48×8 | 8.0 | 48.000 | 44.000 | 40.000 | 4.000 | Quote |
| Tr 52×8 | 8.0 | 52.000 | 48.000 | 44.000 | 4.000 | Quote |
| Tr 60×9 | 9.0 | 60.000 | 55.500 | 51.000 | 4.500 | Quote |
| Tr 70×10 | 10.0 | 70.000 | 65.000 | 60.000 | 5.000 | Quote |
| Tr 80×10 | 10.0 | 80.000 | 75.000 | 70.000 | 5.000 | Quote |
| Tr 90×12 | 12.0 | 90.000 | 84.000 | 78.000 | 6.000 | Quote |
| Tr 100×12 | 12.0 | 100.000 | 94.000 | 88.000 | 6.000 | Quote |
Multiple pitch options: Many Tr diameters are available in more than one pitch. For example, Tr 20 is available in 2mm, 4mm, and 8mm pitch. Always confirm the pitch from the engineering drawing before ordering a gauge — the pitch must be explicitly stated in every Tr thread callout.
Trapezoidal Thread Tolerance Classes
Trapezoidal threads use a tolerance class system similar to ISO metric threads — a number (tolerance grade) and a letter (tolerance position). Uppercase letters (H, G) indicate internal threads; lowercase letters (e, g, h) indicate external threads.
| Class | Thread Location | Fit Type | Typical Application |
|---|---|---|---|
| 7H | Internal (nut/housing) | Standard — most common | General purpose lead screws, machine tool axes |
| 8H | Internal (nut/housing) | Loose | Applications requiring easy assembly or with coatings |
| 9H | Internal (nut/housing) | Very loose | Large backlash acceptable — rough service |
| 7e | External (lead screw) | Standard — most common | General purpose lead screws — mates with 7H nut |
| 7g | External (lead screw) | Close | Precision lead screws, low backlash applications |
| 8e | External (lead screw) | Loose | Coated or plated lead screws |
Default tolerance class: If the drawing shows no tolerance class for a Tr thread, 7H (internal) and 7e (external) are the correct defaults per DIN 103. This is the most widely used combination for general engineering lead screws and provides sufficient clearance for lubrication and thermal expansion in production machinery.
Trapezoidal Thread Gauge Types
Trapezoidal Thread Gauge Inspection Procedure
The GO/NO-GO inspection procedure for Tr threads follows the same principles as standard metric thread inspection, with one additional consideration — the larger pitch and thread depth of Tr threads makes cleaning and lubrication more important than for fine pitch metric threads.
How to Order a Trapezoidal Thread Gauge
To receive an accurate quotation, provide the following information in your first message. Incomplete RFQs delay the quotation process — a complete callout gets a response within 24 hours.
| Required Information | Example | Why It Matters |
|---|---|---|
| Full thread designation | Tr 32×6 | Diameter + pitch both required — cannot be assumed |
| Tolerance class | 7H (internal) or 7e (external) | Different limits for each class |
| Plug or ring gauge | Plug (internal Tr nut) | Internal → plug gauge · External → ring gauge |
| GO only / NO-GO only / full set | Full GO + NO-GO set | Always specify for ring gauges — separate rings |
| Quantity | 2 sets | Affects pricing and lead time |
| Calibration certificate | ISO/IEC 17025 required | Always specify if required |
| Delivery country | Germany / UK / Australia | For shipping cost and Incoterms |
Comparing Tr threads with inch Acme? Our Acme thread profile guide explains the 29° vs 30° difference and why the two need different gauges.
Frequently Asked Questions
Order Trapezoidal Thread Gauges — Tr Plug and Ring
GageTools manufactures Tr thread plug and ring gauges per DIN 103 / ISO 2903 for all standard sizes and tolerance classes. ISO/IEC 17025 calibration certificate available on request. MOQ 1 piece. Custom sizes from drawing. Response within 24 hours.
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