WeldConstraint

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WeldConstraint is used to attach two BaseParts together. The constraint makes sure that the parts stay in the same relative position and orientation to one another, meaning that if one part moves, the other will move the same amount. Even if the two parts are not touching one another, 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 Model tab.

Create button picker indicated in Studio toolbar

This tool will act differently based on how many parts are selected when the tool is activated:

OptionTool Behavior
No parts selectedThe next two parts that are clicked will be welded together. If the same part is clicked twice, no weld will be created.
One part selectedThe next part that is clicked will be welded to the selected part.
Several parts selectedAny parts in the overall selection that are touching or overlapping will be welded together.

Repositioning Welded Parts

Roblox handles moving a welded part differently depending on whether the part was moved using its Position or with 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.

Summary

Properties

Active: boolean

Indicates if the WeldConstraint is currently active in the world.

READ ONLY
NOT REPLICATED
Enabled: boolean

Toggles the constraint on and off.

NOT REPLICATED
Part0: BasePart

The first part connected by the constraint.

NOT REPLICATED
Part1: BasePart

The second part connected by the constraint.

NOT REPLICATED

Methods

Events

Properties

Active

boolean
Read Only
Not Replicated
Read Parallel

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.

Enabled

boolean
Not Replicated
Read Parallel

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.

Part0

BasePart
Not Replicated
Read Parallel

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.

local partA = Instance.new("Part")

local partB = Instance.new("Part")



partA.Position = Vector3.new(0, 10, 0)

partA.Parent = game.Workspace



partB.Position = Vector3.new(0, 10, 10)

partB.Parent = game.Workspace



local weld = Instance.new("WeldConstraint")

weld.Parent = partA

weld.Part0 = partA

weld.Part1 = partB

Part1

BasePart
Not Replicated
Read Parallel

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.

local partA = Instance.new("Part")

local partB = Instance.new("Part")



partA.Position = Vector3.new(0, 10, 0)

partA.Parent = game.Workspace



partB.Position = Vector3.new(0, 10, 10)

partB.Parent = game.Workspace



local weld = Instance.new("WeldConstraint")

weld.Parent = partA

weld.Part0 = partA

weld.Part1 = partB

Methods

Events