How to get the position of the middle of a part?

I started with this but the part just spawned somewhere not in the middle:

local source = script.Parent
local part1 = Instance.new("Part", workspace)
part1.Name = "Test"
part1.Position = Vector3.new(source.Position.x /2,source.Size.y+source.Size.y, source.Position.z / 2)

I wanted to use the midpoint formula but I don't really know how to get the corners of a part either.