DIN 933 is the old German standard for a hexagon head screw that is threaded all the way to the head. It has been replaced by ISO 4017, but the DIN name is still used in trade and on many purchase orders.
For fasteners for construction, size is only the start. You must also specify the property class, the coating and the certificate, because these decide whether the fastener carries the load.
What does DIN 933 cover?
DIN 933 describes the dimensions of a fully threaded hex head screw: head size, thread length and tolerances. Its partly threaded cousin is DIN 931, now ISO 4014. Do not mix them up, because shank length changes how the joint carries shear load.
When ordering, write the thread size, the length, the standard and the property class, for example M12 x 50 DIN 933 class 8.8. The thread is coarse unless you state a fine pitch.
Which property class do you need?
Property class tells you the strength. Classes such as 4.6, 8.8 and 10.9 are defined in ISO 898-1 for carbon and alloy steel fasteners. Stainless steel fasteners follow ISO 3506 with classes such as A2-70. Read fastener grades and standards for how to compare ISO, DIN and ASTM.
Higher classes need more care. Zinc plating of high-strength steel can cause hydrogen embrittlement, so ask how the maker controls it, for example by baking after plating.
What coating suits construction use?
Outdoor and structural work needs corrosion protection. Options include electroplated zinc, hot-dip galvanising and mechanical coatings. Hot-dip galvanising gives a thicker layer than electroplating, and it is usually covered by ISO 10684. Our article on surface treatments: zinc, phosphating and powder coating compares them.
Fastener threads change when a thick coating is applied. Ask how the maker keeps nut and bolt fit, since oversize or undersize tapping may be needed.
What about structural bolting rules?
Structural bolting in steel construction is often covered by separate standards. In Europe, assemblies for structural use are covered by the EN 15048 and EN 14399 series, and CE marking can apply. Do not assume that a DIN 933 screw meets a structural specification.
Rules differ by country and by project. Confirm the requirement with your engineer, authority or conformity adviser, and put it in the purchase order.
How do you check an order?
Ask for test certificates, such as EN 10204 type 3.1, that link to the steel lot. Check head markings: the maker's mark and the property class should be stamped on the head.
Sample each lot for dimensions, hardness and coating thickness. A lab tensile test is worth doing on a first order. Our guide to the document pack your broker will ask for lists the papers to have ready.
Check the thread with a go and no-go gauge on a sample, and measure the head across flats and the length. Reject mixed lots: bolts of different lengths or classes in one carton are a common error. Ask for each size to be packed and labelled separately, with the class, coating and lot number on the carton.
Next step
We shortlist fastener makers, have lots tested and supervise loading. Book a free sourcing review with your size list, class and coating.