RodConstraint not working?

I got this script on the wiki, and It's not working. No errors.

local partA = game.Workspace.PartA
local attachmentA = Instance.new("Attachment", partA)
attachmentA.Position = Vector3.new(0, 0, -1)
 
local partB = game.Workspace.PartB
local attachmentB = Instance.new("Attachment", partB)
attachmentB.Position = Vector3.new(0, .5, 0)
 
local rodConstraint = Instance.new("RodConstraint", partA)
rodConstraint.Attachment0 = attachmentA
rodConstraint.Attachment1 = attachmentB
rodConstraint.Length = 3
 
while wait(2) do
	rodConstraint.Enabled = not rodConstraint.Enabled
end

it's a server script in serverScriptService. It does make the attachments, and it makes the constraint. I have ShowContriants set to true, and I can see the attachments, but not the constraint. It does the enabled thing, but it doesn't do any constraining!