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The joint simulated by phys_ballsocket. Note that Source permits a full 360° of movement since the constraint itself has no physical presence.
Phys ballsocket.png

phys_ballsocket is a point entity available in all Source games. It simulates a rigid connection between the centre of its constrained entities and its own location that prevents them from changing relative distance and makes their rotation point its own location.

Most constraints, if given two entities, will constrain them directly to each other; phys_ballsocket will constrain them to itself. Despite this slightly different behaviour however, the entity still won't remain at a fixed location when two entities are attached. To do: Can you constrain the constraint?

Note.png Note: Torque limit is always 0 (infinite) for this entity.

Example map: sourcesdk_content\hl2\mapsrc\sdk_phys_ballsocket.vmf



Entity 1 (attach1) <targetname>
Entity 2 (attach2) <targetname>
The entities to constrain. Leave one or the other field blank to constrain to the world.
Note.png Note: Only one entity will be constrained, even if several share the given targetname.
Constraint System Manager (constraintsystem) <targetname>
A phys_constraintsystem that this constraint should be a part of. This avoids the "jiggling" caused by constraints applied to the same set of entities fighting with each other.
Force Limit to Break (forcelimit) <float>
Impact force required to break the constraint, in pounds. 0 means infinite. A way of calculating this is to set it to the weight of an object that would break the constraint if it were resting on its objects.
Torque Limit to Break (torquelimit) <float>
Torque required to break the constraint, in pounds*inches. 0 means infinite. A way of calculating this is to multiply any reference mass by the resting distance (from the center of mass of the object) needed to break the constraint.
Play Sound on Break (breaksound) <string>
A sound played when the constraint is broken.
Follow teleport distance (teleportfollowdistance) <float>
If one constrained object teleports more than this many units away, the other will teleport with it.


Name (targetname) <string>
The targetname that other entities refer to this entity by.
Entity Scripts (vscripts) <scriptlist> (in all games since <Left 4 Dead 2>)
Space delimited list of VScript files (without file extension) that are executed after all entities have spawned. The scripts are all executed in the same script scope, later ones overwriting any identical variables and functions.
Script think function (thinkfunction) <string> (in all games since <Left 4 Dead 2>)
Name of a function in this entity's script which will be called automatically every 100 milliseconds (ten times a second) for the duration of the script. It can be used to create timers or to simulate autonomous behavior. The return value (if present) will set the time until the next call.
Note.png Note: Try to avoid expensive operations in this function, as it may cause performance problems.


  • 1: No Collision until break
  • 4: Start inactive
  • 8: Change mass to keep stable attachment to world
  • 16: Do not connect entities until turned on



Force the constraint to break.
Enable the constraint; do this if the constrained objects don't exist when it spawns. Note that broken constraints cannot be turned back on as they have been deleted.
Disable the constraint.


Removes this entity from the world.
Removes this entity and its children from the world.
Note.png Note: Entities already remove orphaned children upon being removed, but this input removes all children on the same frame, being marginally faster than Kill.
AddOutput <string>
Adds a keyvalue/output to this entity. It can be potentially very dangerous, use with care.
KV Format: <key> <value>
I/O Format: <output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
FireUser1 to FireUser4
Fire the OnUser outputs; see User Inputs and Outputs.
Use  !FGD
Same as a player invoking +use; may not do anything depending on the entity. Can also be invoked by firing an output that does not specify an input.
RunScriptFile <script> (in all games since <Left 4 Dead 2>)
Execute a VScript file from disk, without file extension. The script contents are merged with the script scope of the receiving entity.
RunScriptCode <string> (in all games since <Left 4 Dead 2>)
Execute a string of VScript source code in the scope of the entity receiving the input. String quotation may be needed when fired via console.
Bug.png Bug: In <Left 4 Dead 2>, the code is executed in the script scope of the entity that fires the output, not the one receiving the input.
Warning.png Warning: Never try to pass string parameters to a script function with this input. It will corrupt the VMF structure because of the nested quotation marks, which then must be removed manually with a text editor.
CallScriptFunction <string> (in all games since <Left 4 Dead 2>) !FGD
Execute a VScript function in the scope of the receiving entity.
SetLocalOrigin <coordinates> (in all games since <Alien Swarm>) !FGD
Send this entity to a spot in the map. If the entity is parented to something, it will be offset from the parent by this amount.
SetLocalAngles <angles> (in all games since <Alien Swarm>) !FGD
Set this entity's angles.



Fired when the constraint breaks.


OnUser1 to OnUser4
These outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.
OnKilled  (only in Left 4 Dead <Left 4 Dead 2>)
This output fires when the entity is killed and removed from the game.