I second Richard Hull's statement. Here in Silicon Velley, I see VCR fittings crop up more often than anything else. In addition to having a UHV-rated metal to metal seal, they also require zero makeup room, making them useful for work in tight quarters. The price Richard mentions is scarifying, to say the least. I've gotten all my VCR components on the surplus market except for the replacement gaskets, which are a buck to a buck fifty apiece. You can get a gasket retainer for the newer varieties that allows gasket re-use. These are expensive, but probably a plus if you have a joint you know you are going to take apart repeatedly.
Second best, but not bad at all, are Swagelok fittings. These are not UHV rated, but are good for general use, and are considerably less expensive than VCR fittings. These require considerable room for makeup, and this needs to be planned out when you are bending your tubing.
These two fitting types are industry standards, and if you stick to them, you will have an easier time finding compatible valves on the surplus market. Information for both types is available at swagelok.com.
Created on Tuesday, May 08, 2001 11:35 AM EDT by Richard L. Hester