In this guide
DIN 933 and DIN 931 are the two most widely ordered metric hex bolt standards. They look almost identical in a catalogue photo, and buyers often use the names interchangeably, but they are different parts. Ordering the wrong one can mean bolts that don't clamp properly or threads that sit in a shear plane.
The key difference: thread length
| DIN 933 | DIN 931 | |
|---|---|---|
| Thread | Fully threaded, close to the head | Partially threaded, with a plain shank |
| ISO equivalent | ISO 4017 | ISO 4014 |
| Typical use | General assembly, adjustable joints, tapped holes | Joints in shear, hinges, pivot points, structural connections |
| Strength in shear | Threads may sit in the shear plane | Plain shank can carry shear load |
DIN 933 (ISO 4017) is threaded along practically the whole length. DIN 931 (ISO 4014) has a plain, unthreaded portion under the head, and the thread length depends on the bolt diameter and length.
When to choose DIN 933
- The bolt screws into a tapped hole and you need thread engagement at different depths.
- The clamped thickness varies, or you want one length to cover several joint thicknesses.
- General machinery, frames and maintenance stock, where flexibility matters more than shear capacity.
When to choose DIN 931
- The joint is loaded in shear and you want the smooth shank, not the threads, in the shear plane.
- The bolt acts as a pivot or locating pin, where a smooth shank gives better fit and less wear.
- Longer bolts through thick sections, where a full thread is unnecessary and adds cost.
Are DIN and ISO versions interchangeable?
Mostly, yes. ISO 4014 and ISO 4017 replaced DIN 931 and DIN 933 in Europe, but the DIN names are still used every day in trade. There are small dimensional differences in a few sizes (for example, across-flats on M10, M12, M14 and M22 differ between some DIN and ISO editions), which affects which spanner fits. If that matters, state which standard is binding.
Grades and finishes
Both standards are commonly supplied in property classes 8.8, 10.9 and 12.9 in carbon or alloy steel, and in stainless steel A2-70 and A4-70/80. Finishes include plain, zinc plated, hot-dip galvanised and black oxide. See our coatings guide to choose one.
How to order correctly
Write the full description, for example: "Hex bolt ISO 4014 (DIN 931), M16 × 120, property class 8.8, hot-dip galvanised, with ISO 4032 class 8 HDG nuts tapped oversize, 2,000 sets." That single line removes most of the ambiguity a factory would otherwise have to guess.
Need both types, or not sure which your drawing calls for? Send us the drawing and we'll confirm before quoting. Browse our mechanical products.
Frequently asked questions
Is DIN 933 the same as ISO 4017?
Functionally, yes: ISO 4017 is the international standard that replaced DIN 933 for fully threaded hex bolts. A few sizes have slightly different across-flats dimensions between editions, so state which standard is binding if spanner size matters.
Can I use DIN 933 instead of DIN 931?
Sometimes, but not in joints loaded in shear or used as pivots, where the smooth shank of DIN 931 is needed. Check with your design engineer.
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