rojo/.cursor/rules/roblox/en-us/physics/constraints/weld.md

title	description
Weld	WeldConstraint attaches two BaseParts together and ensures they stay in the same relative position and orientation to each other.

A Class.WeldConstraint connects two Class.BasePart|BaseParts and ensures they stay in the same relative position and orientation to each other. Even if the two parts are not touching, you can weld them together.

To attach two `Class.Attachment|Attachments` or `Class.Bone|Bones`, versus two `Class.BasePart|BaseParts`, see [RigidConstraint](../../physics/constraints/rigid.md).

Unique to Class.WeldConstraint are slight behavioral differences in how Studio handles creation and repositioning of welded parts.

When creating a `Class.WeldConstraint` using Studio's [Constraint](../mechanical-constraints.md#create-constraints) button, the tool behaves differently depending on how many `Class.BasePart|BaseParts` are selected when the tool is activated:

• If no Class.BasePart|BaseParts are selected, the next two Class.BasePart|BaseParts clicked will be connected by a new Class.WeldConstraint. If the same Class.BasePart is clicked twice, no constraint will be created.

• If one Class.BasePart is already selected, the next Class.BasePart clicked will be connected to the selected one with a new Class.WeldConstraint.

• If multiple Class.BasePart|BaseParts are selected, those which are touching or overlapping will be automatically welded together by new Class.WeldConstraint|WeldConstraints. Roblox handles moving a welded part differently depending on whether the part was moved through its Class.BasePart.Position|Position or through its Datatype.CFrame.

• If a welded part's Class.BasePart.Position|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 Datatype.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.