M39 × 3 Thread Quick Specifications
| Parameter | Specification | |
| Thread Standard | ISO Metric Threads | |
| Major Diameter | 39 mm | 1.5354 in |
| Pitch | 3 mm | 0.1181 in |
| Pitch Diameter | 37.051 mm | 1.4587 in |
| Minor Diameter | 35.752 mm | 1.4076 in |
| Thread Height | 1.624 mm | 0.0639 in |
| Addendum | 0.974 mm | 0.0383 in |
| Thread Angle | 60° | |
Introduction
The M39 × 3 thread is an ISO metric fine thread designed for applications requiring higher positioning accuracy, improved adjustment resolution, and increased thread engagement within a limited axial length.
Compared with the standard M39 × 4 coarse thread, the M39 × 3 thread features a smaller pitch, allowing more threads to engage over the same distance. This makes it suitable for precision mechanical assemblies where accurate positioning and controlled adjustment are more important than rapid assembly.
This guide provides comprehensive technical information covering M39 × 3 thread dimensions, ISO standards, tolerance classes, engineering considerations, and practical design guidance.
Quick Answer: The M39 × 3 thread is an ISO metric fine thread designed for applications requiring higher positioning accuracy, improved adjustment resolution, and increased thread engagement within a limited axial length.
Understanding M39 × 3 Thread Designation
An M39 × 3 thread is an ISO metric fine thread.
Its designation indicates:
- M= ISO Metric Thread
- 39= Nominal major diameter of 39 mm
- 3= Thread pitch of 3 mm
Unlike the standard M39 coarse thread (4 mm pitch), the M39 × 3 thread provides a finer lead, enabling more precise adjustment and greater thread engagement over the same threaded length.
Understanding the M39 × 3 Designation
Unlike the coarse M39 designation, the pitch must be included because multiple pitch options exist for the same nominal diameter.
Thread Tolerance Classes
Tolerance classes define the permissible dimensional variation of a thread and determine how external and internal threads fit together during assembly.
For ISO metric fine threads such as M39×3, tolerance classes are specified in accordance with ISO 965-1 and ISO 965-2.
A complete designation combines a tolerance grade (numerical value) and a tolerance position (letter).
For example:
M39 × 3 – 6g
where:
- 6 = Tolerance grade
- g = External threadstolerance position
The corresponding internal thread is typically:
M39 × 3 – 6H
Common Tolerance Classes
| Thread Type | Common Class | Typical Application |
| External Thread | 6g | General-purpose screws and bolts |
| Internal Thread | 6H | General-purpose tapped holes and nuts |
| External Thread | 4g6g | Precision mechanical assemblies |
| External Thread | 8g | Loose fit or coated fasteners |
| Internal Thread | 5H | Higher positioning accuracy |
M39 Coarse Thread vs M39 Fine Thread
Many engineers are unaware that M39 is available in more than one pitch.
The two most common versions are:
| Thread | Pitch | Standard Use |
| M39 × 4 | 4 mm | Standard coarse thread |
| M39 × 3 | 3 mm | Fine thread |
M39 × 4 (Coarse)
Advantages:
- Easier assembly
- Better resistance to cross-threading
- Faster installation
- More tolerant of contamination
- Preferred for general-purpose fastening
Typical applications:
- Consumer electronics
- Industrial equipment
- Enclosures
- Control panels
M39 × 3 (Fine)
Advantages:
- More precise axial adjustment
- Greater number of engaged threads within the same length
- Better resistance to self-loosening under certain conditions
Typical applications:
- Optical instruments
- Precision measuring devices
- Fine adjustment mechanisms
- Medical device assemblies
Frequently Asked Questions (FAQ)
Q1. Is M39 × 3 a standard thread?
Yes. M39 × 3 is a standardized ISO metric fine thread defined by ISO standards, although it is less commonly used than the standard M39 × 4 coarse thread.
Q2. Is M39 × 3 the same as M39?
Not exactly.
When a drawing specifies only M39, it usually refers to the standard M39 × 4 coarse thread.
The fine-pitch version must always be written as:
M39 × 3
to avoid manufacturing or purchasing errors.
Q3. What is the difference between M39 × 4 and M39 × 3?
The difference is thread pitch. M39 × 4 has a coarser pitch (4 mm) while M39 × 3 has a finer pitch (3 mm), resulting in more threads per unit length for the fine version.
Q4. Can LCA provide EMI filters with M39 threads?
Yes. LCA supports customized mechanical designs involving metric and inch thread configurations.
Customization options include:
- Thread size
- Housing dimensions
- Electrical parameters
- Sealing structure
- Plating options
Engineering Support CTA: Selecting a threaded EMI filter or feedthrough capacitor? Share the thread standard and size, panel thickness, voltage/current, capacitance, and environmental requirements with LCA engineers. View Thread Mount Feedthrough Filters
Related Engineering Resources
- Unified Thread Standard
- UNC Threads
- UNF Threads
- UNEF Threads
- Metric Threads
- Metric Coarse Threads
- Metric Fine Threads
- #4-40 UNC Thread Dimensions
- 1/4-28 UNF Thread Dimensions
- 5/16-32 UNEF Thread Dimensions
- 5 Thread Dimensions
- M5 Thread Dimensions
- M4 Thread Dimensions
- M6 Thread Dimensions
- M7 Thread Dimensions
- M8 Thread Dimensions
- M9 Thread Dimensions
- M11 Thread Dimensions
- M12 Thread Dimensions
- M14 Thread Dimensions
- M16 Thread Dimensions
- M18 Thread Dimensions
- M20Thread Dimensions
- M22 Thread Dimensions
- M24 Thread Dimensions
- M27 Thread Dimensions
- M30 Thread Dimensions
- M33 Thread Dimensions
- M36 Thread Dimensions
