Rotation

Here's an example of how I do it:

But this was like 1 or 2 years ago so it might be outdated.

me = game.Workspace.CrniOrao

local msh01 = Instance.new("BlockMesh") ---mesh 
msh01.Scale = Vector3.new(1.01,1.01,1.01) ---scale of mesh 
local prt = Instance.new("Part") ---part 
prt.CanCollide = false ---if true then broke 
prt.BrickColor = BrickColor.new("White") --color of part 
prt.Locked = true --locked part 
prt.Name = "Arm_1" --name of part 
prt.Size = Vector3.new(1,2,1) --size of part 
prt.Parent = me ---parent of part 
msh01.Parent = prt ---parent of the mesh 
local w = Instance.new("Weld") ---weld that make part dont fall 
w.Parent = prt --parent of weld 
w.Part0 = prt --The Part Attached To Part1 
w.Part1 = me["Right Arm"] --The Part Attached To Part0 
w.C1 = CFrame.fromEulerAnglesXYZ(0, 0, 0) * CFrame.new(0, 0, 0) --rotation