Tom,

I am not sure what you mean by "Threat" we use this brand and they are very quiet when all connected.

As it has been mentioned more is better when it comes to exhaust. I could never understand why people spend 20K on a laser system and then did not want to get the proper exhaust set-up.

http://www.sears.com/

Do a search for item #00921335000

Mike,

They are made by Delta. You can get the same unit at Lowes under the Delta name for $119.95. I use a couple for my wood working equipment.