DIN 933 vs DIN 931 is a common question when buying stainless steel hex bolts. The main visible difference is thread coverage: DIN 933 describes fully threaded hex-head fasteners, while DIN 931 describes partially threaded hex-head bolts. Matching the diameter and overall length is only the start.
Before changing from one type to the other, compare the fastener with the joint drawing. The position of the thread and plain shank can matter as much as the bolt length.
DIN 933: fully threaded
A DIN 933 fastener has thread along its usable shaft length, apart from the normal manufacturing details near the head and tip. Buyers often call this a full-thread hex bolt. The corresponding modern ISO reference commonly used in catalogues is ISO 4017.
Full threading can provide adjustment along the shaft. It does not establish the correct engagement for your assembly by itself. Confirm the required length and the receiving thread or matching nut against the drawing.
DIN 931: partially threaded
A DIN 931 bolt has a plain shank below the head and a threaded portion towards the end. The corresponding modern ISO reference commonly used in catalogues is ISO 4014. “Half thread” is a common buying phrase, but it does not mean that exactly half of every bolt is threaded.
The actual threaded length must be checked for the selected diameter, overall length and product specification. If the unthreaded section reaches the nut before the joint is clamped, simply choosing a longer bolt may not solve the fit problem.
Check the standard before accepting a substitute
DIN 933 and DIN 931 remain familiar purchasing terms, although those standards have been withdrawn. Catalogues commonly identify ISO 4017 and ISO 4014 respectively alongside them. This cross-reference is a starting point for checking a product, rather than permission to ignore dimensional differences.
If a purchase order names a specific standard or revision, ask the supplier to state exactly what is being offered. Have any substitution reviewed against the drawing before approving it.
Use the drawing to compare thread position
Lay out the joint as a stack: the parts being clamped, the washers and the nut or tapped component. Note the total clamped thickness and any drawing requirement for a plain shank through the joint.
For a replacement, record the old bolt before removing it from the work area. A clear side photograph beside a ruler is useful supporting information, but measured dimensions and the approved drawing should lead the enquiry. Avoid copying a worn or previously substituted fastener without checking the original requirement.
For example, an M10 x 50 full-thread item and an M10 x 50 partial-thread item share a nominal diameter and length. They should still appear as different lines in your comparison because their thread coverage differs.
A five-measurement enquiry checklist
- Nominal thread diameter: include the measurement system.
- Length under the head: record this separately from the head height.
- Thread pitch: state the required pitch rather than relying on a photograph.
- Threaded length: identify the required thread coverage or drawing dimension.
- Clamped thickness: include the assembled stack where the supplier needs it to understand your enquiry.
Then add the stainless steel grade, required property class, standard, quantity and certificate requirement. These are specification details, not extra dimensions, and they belong on the same enquiry.
Request the correct stainless steel hex bolt
Browse our SS hex bolts and compare the SS 304 and SS 316 grade guides. Send your drawing or size schedule to A M Steel in George Town, Chennai. Ask the team to confirm the offered specification and availability before ordering.
Technical references
Product terminology checked against Bossard listings for DIN 933 / ISO 4017 fully threaded fasteners and DIN 931 / ISO 4014 partially threaded bolts.