You need a Presto weight set for a Presto, not a Mirro weight. Not sure your vent pipe will fit the Presto one, either. You can look at Pressurecookeroutlet.com .

You just sit the lid on and don't tighten down. Don't remove anything. Just leave the counter weight or weight off. Use like any other BWB canner.

Is it deep enough to use as a BWB?

Do you not have a lid to anything in your assortment of cookware that will fit the 16 qt canner? You can use the canner lid as LindaLou suggests and just don't tighten it down, or look in your cupboards. I have a universal lid that fits my Mirro 22 qt when using it as a BWB, and have found the lids to two large chicken fryer style skillets work too. I retired one of the skillets, but kept that lid, put it in the basement with my canning things just in case...

Here is a link that might be useful: Lots of places stock universal lids, this one is Walmart

Link below is to the parts that are available for your Presto Model 7B. The 3 piece weight set often discussed here will not work on it because of the shape of the vent pipe. So you will have to have your gauge tested (see ** below) to be safe. Gauges can be off even when new.

You can try ordering one of the newer model vent pipes but you can see how different it is and the threads don't line up so it has to be rethreaded in a machine shop to work. It would allow you to use the Presto 3 piece weight set.

I also don't think that model is deep enough to use as a BWB except for 1/2 pint jars and maybe pints. Definitely not quarts. It is not as deep as the newer 16 qt. models. By the time you add enough water to it to cover the pint jars with 1-2" of water it will likely boil over the top.

It is easy to buy a new rack for your BWB as they are readily available but if you plan to do pressure canning a newer model would serve you better.

** There is a DIY method for testing your new gauge but it isn't officially approved. Do a trial run with the canner and bring it up to pressure where the counter weight you have (piece that sits on the vent pipe) begins to rock steadily. At that point your gauge should read 15.5 lbs. If it does your gauge is accurate. If it does NOT note the reading on the gauge to know how much it is off and then process your food accordingly. This is a do at your own risk solution.

Dave

Here is a link that might be useful: 7B parts