How do I scale the arm in only direction of an axis within a tween?

game.ReplicatedStorage.FruitRemotes.GomuGomu.Pistol.OnServerEvent:Connect(function(player, mousePos, fruit)
    local character = player.Character
    local arm = {character.RightHand, character.RightLowerArm, character.RightUpperArm}
    local animation = character.Humanoid:LoadAnimation(fruit.PistolAnim)
    animation:Play()

    local Tween = game:GetService("TweenService")
    local scalefactor = 3
    local offset
    local dialationCentre = (character.RightUpperArm.Position + character.RightLowerArm.Position + character.RightHand.Position)/3
    local info = TweenInfo.new(
    1,
    Enum.EasingStyle.Linear,
    Enum.EasingDirection.Out,
    0,
    false,
    0
    )
    
    for i,v in pairs(arm) do
        local pos = v.Position
        local offset = pos - dialationCentre
        offset = offset * scalefactor
        
        local Goals =
        {
        Position = dialationCentre + offset;
        Size = Vector3.new(v.Size.X,v.Size.Y * scalefactor,v.Size.Z)
        }
        local gomuTween = Tween:Create(v, info, Goals)
        gomuTween:Play()
    end
    
end)

I'm trying to scale an arm in only one direction of the y-axis, not BOTH with a tween. I keep having the arm scale in both directions of the y-axis. The problem with this is that welding is involved. I heard dilation would help this problem, and I read a forum on how to do it. The problem with the forum is that it shows how to scale in all axis, but I only want one and trying to tween it makes it more difficult as well. I think the problem is how the code is written for the size. I'm sure there's math involved in this, but I really hope I can get someone to help me with this. Thanks!