How do I know what cups and length

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So I have a Miller diamond back torch has 17 on the side of it and I am having issues with the Collet gripping the tungsten and the cup threading all the way in  the cup is about 1.5 inches long and about the size of a nickel   I am using 3/32 red band for exhaust pipe  and dial arc in 2nd gear at 17 on the dial   how do I determine cup size and is 17 series all that fit?  And what does cup length do
Reply:Go to your local welding store and tell them you want parts for a #17 tig torch. Cup size will depend on joint type, material and amperage. Take all the parts off the torch. Screw collet body into torch head. Screw cup in over the collet body. Drop collet split side first into the back of the torch. Push tungsten into collet. Screw backcap into back of torch. Everything should be seated with just finger tight twisting.If the collet still doesn't grip the tungsten check to make sure both collet and collet body are the right size for the tungsten.Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power) Hobart MIG
Reply:I can sympathize with anyone having issues getting the tungsten to tighten down. Minor differences in design across manufacturers, even same brand or something as seemingly benign as an after market back cap, can mess things up. I recommend taking torch to lws and purchase the parts that you're able to test to work together.
Reply:Some of the chinese tungsten is .001-.002" undersize on the diameter, making it hard to tighten down properly.
Reply:The "17" is the torch size.  Use that number when shopping for the accessories.  When I first started to TIG, I did not realize that there were different size collets for different size tungsten.    You can get a 3/32 tungsten in a collet for 1/8, but it will not hold it  well.   You and also force a 3/32 tungsten into a collet that is too small, but that will not tighten down well.There should be numbers stamped into the side of the collet.  Make sure that they match the diameter of your electrode.The cup size depends on the thickness of the metal you are welding.   A bigger cup will allow more argon flow and provide shielding over a larger area.   There are charts online that give you a cup - thickness - electrode - gas flow cross reference.  Sometimes a smaller cup is used to conserve gas or to allow you to reach into tight areas.  Dan----------------------------Measure twice.  Weld once.  Grind to size.MIG:  Lincoln SP100 TIG/STICK:  AHP Alphatig 200X