On the heat sinks you will run across both sheet style and extruded. The extruded looks like it has been pushed thru a die and the sheet style has the "fins" pinned to the base. Anything tubular should be extruded but it depends on your yard. Some heatsinks from TV's are just cast alum. that has been bent in a right angle. If you break off a piece you should see kind of a rough inside.