In aerospace manufacturing, precision is non-negotiable. Yet one of the most common—and costly—mistakes still comes down to something as basic as using the wrong fastener system. Whether you’re dealing with imperial or metric fasteners, getting the specifications right from the outset helps avoid rework, delays and compromised safety.
At JP Aero, we specialise in supplying aerospace-grade fasteners that conform to both metric and imperial standards—ensuring seamless integration, whatever your specification.
Metric vs. Imperial Fasteners: Why the Difference Matters
For many engineers, fasteners are just components—until they cause a failure. The choice between metric and imperial fasteners affects every detail of design, procurement, assembly and maintenance. Misalignment between metric thread and threads per inch (TPI) can lead to stripped threads, compromised joints or, worse, full structural failure.
Metric fasteners use the ISO standards system, with specifications like M6 or M12 referring to the bolt’s diameter in millimetres. Imperial fasteners, on the other hand, follow the Unified Thread Standard (UTS), with designations such as ¼-20 (¼ inch diameter, 20 TPI). They’re not interchangeable—and guessing is never an option.
Understanding Metric Bolts, Thread Types and Sizes
Metric bolts are commonly used across global aerospace manufacturing due to their compatibility with international standards. Their sizing system is logical and straightforward, expressed in millimetres. For example:
- M8 x 1.25 x 50 refers to an 8mm diameter bolt, with a 1.25mm thread pitch and a length of 50mm.
The metric thread design offers consistent, repeatable engagement—especially valuable in high-tensile applications where full thread bolts are required for maximum grip and durability. Available in stainless steel and other aerospace-grade alloys, these fasteners are ideal for resisting vibration, corrosion and high temperatures.
Metric fasteners are also easier to source in bulk quantities, especially for international projects. At JP Aero, our range of metric bolts includes hex bolts, set screws, grub screws and other specialised components—backed by clear specifications for confident ordering.
Common Imperial Fasteners and Their Applications
Imperial fasteners, still prevalent in legacy aerospace systems—particularly in North America—are defined by inches and TPI. Typical applications involve:
- ¼-20 UNC hex bolts for general structural use
- 10-32 UNF screws for precision assemblies
- Set screws and nuts for equipment requiring finer thread control
A key challenge arises when projects mix systems—using imperial fasteners on components designed with metric tolerances. This is where conversion errors happen, especially when thread pitch, drill sizes or bolt diameters are incorrectly matched.
Products Built for Precision—Whatever the System
At JP Aero, our fastening range includes both metric and imperial products engineered to meet the highest aerospace standards. Our catalogue includes:
- Screws and bolts in stainless steel and high-tensile materials
- Matching nuts, washers and components
- ISO-standard and UTS-compatible options
- Custom and off-the-shelf solutions, available in bulk quantities
Whether you’re replacing a single fastener or equipping a full production line, we help ensure that every detail meets spec—from threads to material grade.
Avoiding Costly Mistakes: Thread Standards and Interchangeability
Conversion between metric and imperial isn’t just about swapping sizes. Thread forms, tolerances and load ratings differ. Even visually similar fasteners can have incompatible threads, leading to dangerous mismatches. Key points to remember:
- A 6mm bolt is not equivalent to a ¼-inch bolt—they differ in thread pitch and diameter.
- Tapping holes for one system and inserting bolts from another can strip threads or deform parts.
- ISO standards and UTS systems define not only size but also fit class, plating requirements and strength ratings.
It’s essential to confirm the correct standard before placing your order—or beginning assembly.
JP Aero: Precision Fastening Products with Global Compatibility
With decades of experience in aerospace fasteners and over 35,000 product lines in stock, JP Aero helps clients avoid costly errors by supplying metric and imperial components built to the highest standards. From high-tensile hex bolts to full thread bolts, set screws, grub screws and more, we deliver precision-engineered products for aerospace and other critical industries—on time, worldwide.
Explore our full range of imperial and metric fasteners—or speak with a specialist about your technical requirements today.