These are Metal Type IV audio cassette tapes. These are custom made, about 60 minutes in length (30 minutes per side), high quality metal tapes recorded on once. Some of the tapes have black transport parts. Others have transparent transport parts. They are screwed together in order to make any future repairs possible and easy. They were made with high quality TDK MA tape stock. Currently they have pre-recorded talks from the 1960s-1970s on them. You will need to cover the record tabs before you can use them. Just put a small piece of tape over the outside half of the rectangle cut outs on each side of the top of the cassette. ... but you're buying Metal Tape, you know your way around tapes.
*important- as I mentioned, these are "about" 60 minutes, these are not retail consumer tapes. they are custom wound, 60 minute TDK MA, because they are custom wound, most will be 60 minutes, some might be 55 minutes, some might be 65 minutes.
If you don't like putting tape over the record cut outs, search this site or other sites for "cassette tape plugs". They are just a few cents, I prefer to just use a small piece of painters tape.