What is the heatsink to be used for?
If its for LED's you can use 1" Aluminum U channel. I have a 4 ft 72 LED array and at 100% my channels are only 120F with no fans.
I got my U channels in 8ft sections from Princess Auto.
You could always place them side by side with heatsink compound on the mating edges. That way you can make the size you want and you will create cooling fins on the backside of the heatsink. Its super light too.
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