I found the Solution here: Introduction to Tweening Models
local offset = primaryPart.CFrame:ToObjectSpace(boundPart)
primaryPart.CFrame = primaryPart.CFrame * CFrame.new(1, 2, 3)
boundPart.CFrame = primaryPart.CFrame:ToWorldSpace(offset)
-- You can also use CFrame inverse, which is what ToObjectSpace is internally
primaryPart.CFrame = primaryPart.CFrame * CFrame.new(1, 2, 3)
boundPart.CFrame = primaryPart.CFrame:Inverse() * boundPart.CFrame
SetPrimaryPartCFrame() - Is DEPRECATED Method & not Recommended for Use, due to Wrong Calculating of Offset.