Why won't anything weld to player's arms?

I'm having trouble welding anything to the player's arms. In a server script, I have a script that's supposed to put a ParticleEmitter inside the player's RightUpperArm and LeftUpperArm. But for some reason, it doesn't get put inside. I tried welding a normal brick to the arm, as well, and that didn't, either. When I replace "RightUpperArm" with "HumanoidRootPart," however, everything works fine, and it's put inside the rootpart like normal. There's a few prints I threw in there, and they both print out just fine, so I'm not sure why it doesn't work.

Here's the script:

game.Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(char)

		local drip = game.ServerStorage.DripParticles:Clone()
		drip.Parent = char:WaitForChild("RightUpperArm")
		print("Drip1 Cloned")
		local drip2 = game.ServerStorage.DripParticles:Clone()
		drip2.Parent = char:WaitForChild("LeftUpperArm")
		print("Drip2 Cloned")
	
	end)
end)

That's not the correct way to weld something. This would be it. Note that I instantiate a Weld, set its properties and parent it to the thing to weld, and then parent this thing to workspace.

local thingToWeld = ReplicatedStorage.Thing:Clone()

-- Make sure these properties are false if you don't want issues
thingToWeld.Anchored = false
thingToWeld.CanCollide = false

local character = player.Character or player.CharacterAdded:Wait()

local weld = Instance.new('Weld')
weld.Part0 = thingToWeld
weld.Part1 = character.PrimaryPart
weld.C0 = character.PrimaryPart.CFrame
weld.C1 = character.PrimaryPart.CFrame
weld.Parent = thingToWeld

thingToWeld.Parent = character

Glad to help :) remember to accept the answer if you find this useful! Thank you <3