Be sure to check the Cooking forum!

Here is a link that might be useful: Cooking forum

For GOOD information on this Pressure Cooker/Canner, ONE PLACE to look is here:
Link: http://ths.gardenweb.com/forums/load/cookware/msg10142458877.html

Perhaps this is a better way to provide the Link?

Here is a link that might be useful: Updating a National Pressure Cooker/Canner

I've seen two kinds of old nationals. There's the gasketless one with the bolts that secure the lid and there's one with a twist to lock lid that requires a gasket.

I am looking at getting a gasketed one because it's the most like my old Presto 4 quart which I am familiar with and find easy to use.

I decided on old rather than new for my big pressure cooker because they seem heavier and more well made. It's also easy to find gaskets and over-pressure plugs for them too.