M39 Thread Quick Specifications
| Parameter | Specification | |
| Thread Standard | ISO Metric Threads | |
| Major Diameter | 39 mm | 1.5354 in |
| Pitch | 4 | 0.1575 in |
| Pitch Diameter | 36.402 mm | 1.4331 in |
| Minor Diameter | 34.67 mm | 1.365 in |
| Thread Height | 2.165mm | 0.0852 in |
| Addendum | 1.299 mm | 0.0511 in |
| Thread Angle | 60° | |
Introduction
The M39 thread is one of the most widely used ISO metric screw threads for precision fastening in electronics, automation, instrumentation, medical devices, robotics, telecommunications, and industrial equipment. Defined by the ISO metric thread system, it provides excellent interchangeability and global compatibility across components manufactured to international standards.
This engineering guide provides comprehensive technical information for the M39 metric thread, including thread designation, major diameter, pitch diameter, minor diameter, tolerance classes.
Whether you are designing a new product, selecting fasteners, machining threaded holes, or specifying mounting interfaces for EMI filters and feedthrough capacitors, this page serves as a practical engineering reference.
Quick Answer: The M39 thread is one of the most widely used ISO metric screw threads for precision fastening in electronics, automation, instrumentation, medical devices, robotics, telecommunications, and industrial equipment.
M39 is an ISO metric thread designation where:
- Mindicates an ISO metric screw thread.
- 39indicates a nominal major diameter of 39 mm.
Unless otherwise specified, M39 normally refers to the coarse pitch version with a 4 pitch.
Understanding the M39 Thread Designation
Unlike Unified threads such as 4-40 UNC or 6-32 UNC, metric thread designations are much simpler.
When pitch is omitted, the designation automatically refers to the standard coarse pitch.
Therefore:
- M39= M39 × 4
If a fine pitch is used, it must be specified explicitly.
For example:
- M39× 4 (Coarse)
- M39× 5 (Fine)
M39 Thread Tolerance Classes
Thread tolerance defines the allowable variation in thread dimensions and determines how tightly an external thread fits with its mating internal thread. Selecting the appropriate tolerance class ensures smooth assembly, adequate preload, and reliable long-term performance.
For ISO metric threads, tolerance classes are specified in accordance with ISO 965-1 and ISO 965-2.
A complete tolerance designation consists of:
- Tolerance Grade(numerical value)
- Tolerance Position(letter)
For example:
M39 × 4 – 6g
where:
- 6 = Tolerance grade
- g = Tolerance position for external threads
Likewise:
M39 × 4 – 6H
is the standard designation for an internal thread.
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 | 7H | Increased assembly clearance |
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 | Standard coarse thread |
| M39 × 1.5 | 1.5 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 × 1.5 (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
Frequently Asked Questions (FAQ)
Q1. Is M39 the same as 1 9/16 – 6 6-UN?
No. Although M39 and 1 9/16 – 6 6-UN have similar physical sizes, they are different thread systems.
Q2. What tolerance class is normally used for M39 threads?
The most common general-purpose tolerance pairing is:
External thread: M39 × 4 – 6g
Internal thread: M39 × 4 – 6H
This combination provides a good balance between:
- Manufacturing cost
- Interchangeability
- Assembly reliability
Q3. What is the difference between M39 × 4 and M39 × 1.5?
The difference is thread pitch.
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
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