What is a weld-on ball joint?
A ball seated in a housing, called the socket or retainer, with the housing welded into the structure. The housing is typically a weldable carbon steel part, and the same pivot is also sold as a "weldable ball joint" or a "weld-in ball socket" (see the weld-on ball joint guide). Unlike a rod end there is no threaded shank: the joint becomes a fixed pivot in the structure. In effect it is the head of a rod end whose shank has been replaced by a body that you weld, for a permanent, non-adjustable connection. With no thread there is none to loosen or strip. The welding heat can reach the parts inside, so the welding must be controlled (Q1-04).
Which construction is it: a ball on a pin, or a ball stud?
Check this first, because the load path depends on it.
A ball with a bore, on a pin. The ball has a hole through it. A pin passes through the hole and is held by the mating parts, such as the two ears of a clevis or the eye of a link. The load goes from the pin into the ball through the bore, from the ball into the housing, and from the housing into the weld. The force that pushes the ball out of the housing acts along the bore axis, which is the pin axis. Tractor lift-arm sockets and top-link ends are this type (Q1-02), and so is a rod end head with the shank left off. Most weld-on sockets on machinery are this type.
A ball stud. The ball and a stem are one piece. The stem carries the load out of the joint, and the socket only holds the ball. Many linkage ball-and-socket joints are built this way. The pull-out force acts along the stem, not along a bore, and the part that gets replaced is usually the stud.
The words overlap. Some supplier pages call the pinned ball in the first type a "ball stud", although in the wider trade the term usually means the second type. When a drawing or listing uses the word, look for a hole through the ball. If there is one, it is a ball on a pin.
What are the different names?
| Name | What it usually means |
|---|---|
| Weld-on ball joint, weld-in ball joint | The whole pivot: the housing to be welded and the ball that pivots in it |
| Weld-on ball socket | The housing, or socket, that is welded in. Tractor parts catalogues list weld-on lift arm ball sockets and top link replacement ends in this form |
| Weld-on ball end | A ball-ended fitting that is welded onto the end of a link or arm. The name is used loosely, so check the drawing |
Treat the names as labels and read what the maker supplies: the housing only, the housing with the ball, or the ball with a pin (Q1-02).
What do shouldered and non-shouldered mean?
Catalogues give both styles:
- Shouldered. A machined shoulder locates the joint against the mounting surface and sets the standoff. It controls the insertion depth and the alignment when the part is positioned for welding. Choose it when the joint must sit at an exact height or face a machined register.
- Non-shouldered. A straight sleeve that welds in flush. It is the simplest, most flexible package for fixtures and structures where the welder sets the position.
Is a weld-on ball joint used on a fabricated chassis or a race-car link?
Sometimes, but it is not the usual choice there. Links on a tube chassis normally need to be adjustable in length and replaceable, so they end in a threaded rod end screwed into a weld-in tube adapter (see the tube adapters page). A weld-on ball joint suits only a fixed pivot that will never need adjusting or changing: a bracket pivot on a self-built trailer, a rig frame or a tube structure. Because the joint is permanent, replacing a worn one means cutting into the tube or bracket it was welded to (Q1-08).
If you want a weld-on ball joint on a vehicle for the same reason a farm arm uses one, a pivot that is fixed and has no thread to loosen, the questions in this article still apply: which construction it is, and whether the mounting needs a shoulder. For the part itself, see the weld-on ball joint page. For a link in a steering or suspension system, the chassis designer decides the joint type and the welding requirements.
When is a weld-on ball joint the wrong choice?
When the pivot must be replaceable. A welded joint is permanent and cannot be serviced after welding. If the pivot has to be changed, use a rod end or a clevis instead (K05-Q1-03). Sizing and welding mistakes are covered in Q1-03 and Q1-04.