Buyers often assume a headed shear connector and a threaded weld stud come from different worlds. They do not. Both are covered by the same standard, ISO 13918, welded by the same process, on the same machine, with the same kind of ceramic ferrule. What separates them is what happens at the top of the stud, and that decides everything about where each one is used.
ISO 13918 covers studs and ceramic ferrules for arc stud welding. Within it, the studs made by drawn arc welding with a ceramic ferrule — the process used on structural steel — are identified by two-letter symbols:
SD is the headed shear connector everyone knows from composite decks. PD, RD and UD are the ones most people in India have never been offered, even though they come off the same production line and weld with the same gun.
The standard also covers types for short-cycle welding and for tip-ignition welding, which use thinner studs on sheet metal. Those are a different trade and are not discussed here.
A headed shear connector transfers horizontal shear between a steel girder and a concrete slab so the two act as one composite section. But shear is only half its job. As the slab deflects it also tries to lift away from the steel, and the forged head, embedded in the concrete, is what stops it. Shear and uplift, in one piece, with nothing to assemble.
That is why ISO 13918 controls head diameter and head thickness for the SD type. The head is not a convenience. It is the anchorage.
A threaded stud has no head, and therefore no anchorage of its own. It is not a shear connector and should not be substituted for one. What it provides is a welded thread — a fixing point on a steel surface where drilling is impossible, unwanted, or would weaken the section.
A threaded stud is welded to the parent steel and then something is bolted onto it. The load path runs through the thread in tension and shear, taken by a nut, not by concrete. That difference produces a completely different set of applications:
Two things follow from this. Because there is no drilling, the parent section keeps its full cross-section and there is no hole to seal or to become a corrosion path. And because the weld is made in about a second by a gun rather than by a welder laying a fillet, a large number of fixings can be placed quickly and consistently.
The thread runs along the shank and the weld end is left plain. The weld base is close to full nominal diameter, so it needs the welding energy that diameter demands. This is the general-purpose type.
The weld end is turned down below the thread, so the same thread size welds with a smaller melt pool. That is not a trivial detail. Less energy means a smaller welding unit, a smaller heat-affected zone, and the ability to weld onto thinner parent material than the same thread size would otherwise allow. It also takes a different, smaller ferrule. Where a contractor is fixing an M16 thread to a relatively thin flange and finding the weld marginal, RD is usually the answer.
A plain pin with no thread and no head. Used as a locating pin, an anchor pin, and widely for insulation retention where a plain shank with a speed clip is enough. Because it has no head, it gives no uplift restraint, which is exactly why it is not a shear connector.
The ceramic ferrule contains the molten pool, shields the arc, and shapes the weld collar that forms around the base. It is broken off and discarded after welding. ISO 13918 gives three ferrule families for the drawn arc types:
The practical point for a buyer: a UD stud and an SD shear connector of the same diameter share a ferrule, but a PD threaded stud of the same thread size does not. Ordering threaded studs and assuming your existing shear connector ferrules will fit is a common and expensive mistake on site.
A stud has to be weldable before it has to be strong. Low-carbon steel welds predictably; as carbon rises the heat-affected zone hardens and the weld becomes prone to cracking. ISO 13918 draws the line at a carbon content of about 0.20% for non-alloyed steel studs, and specifies free-cutting steels as generally unsuitable.
That is why threaded weld studs are normally supplied to property class 4.8 rather than to 8.8 or 10.9. It looks like a low grade next to a structural bolt, but it is the grade the process allows. If your design needs 8.8 or above at that fixing, the answer is a bolt through a drilled hole, or a welded plate with a tapped or clearance hole — not a higher-grade weld stud.
Shear connectors sit in a different material group again: a weldable mild steel with specified minimum tensile and yield values and a minimum elongation, chosen so the stud can deform in the concrete rather than fracture.
| Headed shear connector (SD) | Threaded stud (PD / RD) | Unthreaded stud (UD) | |
|---|---|---|---|
| What it does | Transfers shear between steel and concrete | Provides a welded thread to bolt onto | Provides a plain welded pin |
| Resists uplift | Yes — the head anchors in concrete | Through the nut, not the stud | No |
| Demountable | No | Yes | No |
| Ferrule | UF | PF (PD) / RF (RD) | UF |
| Typical use | Composite bridge and building decks, embed plates | Cladding, insulation, brackets, demountable fixings, plant mounting | Insulation pins, locating and anchor pins |
| Property class | Weldable mild steel grades | 4.8 as standard | 4.8 as standard |
ISO 13918 sets out a designation format so an order is unambiguous. It carries the standard number, the type symbol, the thread or diameter, the length after welding, and the material or property class. For a threaded stud it reads in this shape:
And for an unthreaded stud, where a plain diameter replaces the thread designation:
The length quoted is the length after welding, which is shorter than the stud you take out of the box. Some material is consumed in the arc and some is pushed out into the weld collar. If you order to the pre-weld length by mistake, every fixing on the job ends up short. State clearly which length you are quoting.
Ferrules are designated separately, by their form and the stud diameter they suit.
S.R. Forgings manufactures all three drawn arc types at Focal Point, Ludhiana:
We also manufacture headed shear connector studs to ISO 13918 from 13 mm to 31.75 mm diameter and up to 1016 mm long, and PSR punching shear studs and stud rails. Threads elsewhere in our range are rolled rather than cut, on hydraulic thread rolling machines up to ø100 mm.
If you are specifying weld studs and are not certain whether the application needs a shear connector, a threaded stud or a reduced-shaft type, send us the detail and the parent material thickness. That question is easier to settle before the order than after the first weld fails a bend test.
PD, RD and UD studs M10 to M24 with matched ceramic ferrules, and headed shear connector studs from 13 mm to 1¼ inch in lengths to 40 inch. Standard sizes or to your drawing, with test certificates.
Send your requirementDimension tables, tolerances and mass figures for each stud type are given in ISO 13918 itself, available from ISO or your national standards body. Related reading: shear connector studs vs PSR studs · shear connector studs in modern construction · all articles.