How do I scale a body part in ONE direction of ONE axis?

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 = v.Size * Vector3.new(1,scalefactor,1)
		}
		local gomuTween = Tween:Create(v, info, Goals)
		gomuTween:Play()
	end
	
end)

I'm trying to scale an arm with a tween, however, I only want the arm to scale in one direction of an axis. Not BOTH. It should look like an arm-stretching forward. For some reason it will always scale both directions. I read a forum that dilation could work fixing this problem, but it goes over scaling all axis, so I'm not sure how to do this. Please, if you know a way to solve this, please answer. Been stuck with this problem for almost a day now.

Your looking for Resize. It functions similar to this:

Part:Resize(Enum.NormalId.Direction, 1) 

Replace Direction with the face you want to resize and replace the # with the amount of studs you want to expand it by.

Though I'm not 100% sure it will work with a tween. But its still worth trying.