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Source: Roblox Creator Hub · CC BY 4.0 · View source · Code samples: MIT Imported 2026-10-03. Formatting adapted for this site.

WeldConstraint

Inherits from: Instance → Object

WeldConstraint connects two BaseParts and ensures they stay in the same relative position/orientation to each other, meaning that if one part moves, the other moves the same amount. Even if the two parts are not touching, they can be welded together.

The most common way to create a weld constraint is by selecting Weld through Studio's Create menu in the toolbar's Model tab.

Note that this tool behaves differently depending on how many BaseParts are selected when the tool is activated:

If no BaseParts are selected, the next two BaseParts clicked will be connected by a new WeldConstraint. If the same BasePart is clicked twice, no constraint will be created.
If one BasePart is already selected, the next BasePart clicked will be connected to the selected one with a new WeldConstraint.
If multiple BaseParts are selected, those which are touching or overlapping will be automatically welded together by new WeldConstraints.

Repositioning Behavior

Moving a welded BasePart behaves differently depending on whether the part was moved through its Position or through its CFrame.

If a welded part's Position is updated, that part will move but none of the connected parts will move with it. The weld will recalculate the offset from the other parts based on the moved part's new position.
If a welded part's CFrame is updated, that part will move and all of the connected parts will also move, ensuring they maintain the same offset as when the weld was created.

Inherits from: Instance

Memory category: BaseParts

Properties

Name	Type / Returns	Description
WeldConstraint.Active	boolean	Indicates if the WeldConstraint is currently active in the world.
WeldConstraint.Enabled	boolean	Toggles the constraint on and off.
WeldConstraint.Part0	BasePart	The first part connected by the constraint.
WeldConstraint.Part1	BasePart	The second part connected by the constraint.

Inherited from Instance

Name	Type / Returns	Description
Instance.Archivable	boolean	Determines if an `Instance` and its descendants can be cloned using `Instance:Clone()`, and can be saved/published.
Instance.archivable	boolean
Instance.Capabilities	SecurityCapabilities	The set of capabilities allowed to be used for scripts inside this container.
Instance.IsInSandbox	boolean	Indicates whether the instance is inside a sandboxed container.
Instance.Name	string	A non-unique identifier of the `Instance`.
Instance.Parent	Instance	Determines the hierarchical parent of the `Instance`.
Instance.PredictionMode	PredictionMode	Reflects the client-side prediction mode applied to the instance under server-authoritative physics.
Instance.RobloxLocked	boolean	A deprecated property that used to protect `CoreGui` objects.
Instance.Sandboxed	boolean	When enabled, the instance can only access abilities in its `Capabilities` list.
Instance.UniqueId	UniqueId	A unique identifier for the instance.

Inherited from Object

Name	Type / Returns	Description
Object.ClassName	string	A read-only string representing the class this `Object` belongs to.
Object.className	string

WeldConstraint.Active

True if the WeldConstraint is currently active in the world.

If the WeldConstraint or one of its parts is not in Workspace the weld will be inactive.

Rigid joints like Weld, Snap, WeldConstraint, Motor, or Motor6D may also be disabled due to conflicts with other rigid joints, such as joints between the same two parts or indirect cycles in the weld graph. Joints disabled this way may be re-enabled later when another joint or part is added or removed.

Duplicate WeldConstraints do not conflict because WeldConstraints derive their internal CFrames from the relative positions of their parts when they are enabled and all update when BasePart.Position or BasePart.Orientation is set on a part. The spanning tree may still disable them if they are redundant or form a cycle.

Field	Value
type	boolean
tags	["ReadOnly","NotReplicated"]
security	{"read":"None","write":"None"}
thread safety	ReadSafe
category	Behavior
serialization	{"can_load":false,"can_save":true}
capabilities	["Physics"]
simulationAccess	true

WeldConstraint.Enabled

The Enabled property of a WeldConstraint sets whether the constraint is active or not. When this property is set to true, if the constraint's WeldConstraint.Part0 and WeldConstraint.Part1 properties are set, then the constraint will ensure that its two connected parts will be locked together.

Field	Value
type	boolean
tags	["NotReplicated"]
security	{"read":"None","write":"None"}
thread safety	ReadSafe
category	Behavior
serialization	{"can_load":true,"can_save":false}
capabilities	["Physics"]
simulationAccess	true

WeldConstraint.Part0

The Part0 and WeldConstraint.Part1 properties of a WeldConstraint set which two BasePart the weld connects. As soon as both properties are set and the weld is WeldConstraint.Enabled, the weld will lock the two parts together.

If Part0 or Part1 are ever set to new parts, then the WeldConstraint will instantly link the new part. The old part will no longer be constrained.

Field	Value
type	BasePart
tags	["NotReplicated"]
security	{"read":"None","write":"None"}
thread safety	ReadSafe
category	Parts
serialization	{"can_load":true,"can_save":false}
capabilities	["Physics"]
simulationAccess	true

Code samples: View on Creator Hub (WeldConstraint-Part0).

WeldConstraint.Part1

The WeldConstraint.Part0 and Part1 properties of a WeldConstraint set which two BasePart the weld connects. As soon as both properties are set and the weld is WeldConstraint.Enabled, the weld will lock the two parts together.

If Part0 or Part1 are ever set to new parts, then the WeldConstraint will instantly link the new part. The old part will no longer be constrained.

Field	Value
type	BasePart
tags	["NotReplicated"]
security	{"read":"None","write":"None"}
thread safety	ReadSafe
category	Parts
serialization	{"can_load":true,"can_save":false}
capabilities	["Physics"]
simulationAccess	true

Code samples: View on Creator Hub (WeldConstraint-Part1).

Methods

Inherited from Instance

Name	Type / Returns	Description
Instance:AddTag	()	Applies a tag to the instance.
Instance:children	Instances	Returns an array of the object's children.
Instance:ClearAllChildren	()	This method destroys all of an instance's children.
Instance:Clone	Instance	Create a copy of an instance and all its descendants, ignoring instances that are not `Archivable`.
Instance:clone	Instance
Instance:Destroy	()	Sets the `Instance.Parent` property to `nil`, locks the `Instance.Parent` property, disconnects all connections, and calls `Destroy()` on all children.
Instance:destroy	()
Instance:FindFirstAncestor	Instance?	Returns the first ancestor of the `Instance` whose `Instance.Name` is equal to the given name.
Instance:FindFirstAncestorOfClass	Instance?	Returns the first ancestor of the `Instance` whose `Object.ClassName` is equal to the given className.
Instance:FindFirstAncestorWhichIsA	Instance?	Returns the first ancestor of the `Instance` for whom `Object:IsA()` returns true for the given className.
Instance:FindFirstChild	Instance?	Returns the first child of the `Instance` found with the given name.
Instance:findFirstChild	Instance
Instance:FindFirstChildOfClass	Instance?	Returns the first child of the `Instance` whose `ClassName` is equal to the given class name.
Instance:FindFirstChildWhichIsA	Instance?	Returns the first child of the `Instance` for whom `Object:IsA()` returns true for the given className.
Instance:FindFirstDescendant	Instance?	Returns the first descendant found with the given `Instance.Name`.
Instance:GetActor	Actor?	Returns the `Actor` associated with the Instance, if any.
Instance:GetAttribute	Variant	Returns the value which has been assigned to the given attribute name.
Instance:GetAttributeChangedSignal	RBXScriptSignal	Returns an event that fires when the given attribute changes.
Instance:GetAttributes	Dictionary	Returns a dictionary of the instance's attributes.
Instance:GetChildren	Instances	Returns an array containing all of the instance's children.
Instance:getChildren	Instances
Instance:GetDebugId	string	Returns a coded string of the debug ID used internally by Roblox.
Instance:GetDescendants	Instances	Returns an array containing all of the descendants of the instance.
Instance:GetFullName	string	Returns a string describing the instance's ancestry.
Instance:GetStyled	Variant	Returns the styled or explicitly modified value of the specified property, or else the default property value if it hasn't been styled/modified.
Instance:GetStyledPropertyChangedSignal	RBXScriptSignal	Returns an event that fires when the given style property changes on the instance.
Instance:GetTags	Array	Gets an array of all tags applied to the instance.
Instance:HasTag	boolean	Check whether the instance has a given tag.
Instance:IsAncestorOf	boolean	Returns true if an `Instance` is an ancestor of the given descendant.
Instance:IsDescendantOf	boolean	Returns `true` if an `Instance` is a descendant of the given ancestor.
Instance:isDescendantOf	boolean
Instance:IsPropertyModified	boolean	Returns `true` if the value stored in the specified property is not equal to the code-instantiated default.
Instance:QueryDescendants	Instances	Returns an array containing all descendants of the instance that match the `selector` string.
Instance:Remove	()	Sets the object's `Parent` to `nil`, and does the same for all its descendants.
Instance:remove	()
Instance:RemoveTag	()	Removes a tag from the instance.
Instance:ResetPropertyToDefault	()	Resets a property to its default value.
Instance:SetAttribute	()	Sets the attribute with the given name to the given value.
Instance:WaitForChild	Instance	Returns the child of the `Instance` with the given name. If the child does not exist, it will yield the current thread until it does.

Inherited from Object

Name	Type / Returns	Description
Object:GetPropertyChangedSignal	RBXScriptSignal	Get an event that fires when a given property of the object changes.
Object:IsA	boolean	Returns true if an object's class matches or inherits from a given class.
Object:isA	boolean

Events

Inherited from Instance

Name	Type / Returns	Description
Instance.AncestryChanged		Fires when the `Instance.Parent` property of this object or one of its ancestors is changed.
Instance.AttributeChanged		Fires whenever an attribute is changed on the `Instance`.
Instance.ChildAdded		Fires after an object is parented to this `Instance`.
Instance.childAdded
Instance.ChildRemoved		Fires after a child is removed from this `Instance`.
Instance.DescendantAdded		Fires after a descendant is added to the `Instance`.
Instance.DescendantRemoving		Fires immediately before a descendant of the `Instance` is removed.
Instance.Destroying		Fires immediately before (or is deferred until after) the instance is destroyed via `Instance:Destroy()`.
Instance.StyledPropertiesChanged		Fires whenever any style property is changed on the instance, including when a property is set to `nil`.

Inherited from Object

Name	Type / Returns	Description
Object.Changed		Fires immediately after a property of the object changes, with some limitations.