USB Thumb drives

[ErikJan]

I have three (old) USB2 thumb drives. I tried to wipe/zero and then format them.
They look completely identical, let's call them A, B and C. They show up in Explorer with capacities of (all FAT)
A: 978Mb
B: 975MB
C: 1800MB

In write tests A and B show about the same performance but C is twice as slow. There's one partition on all three as far as I can see.
I think I know C had a boot image loaded one day.
I used tools like USBDeview (NirSoft) and USBDriveInfo (Uwe Sieber) but didn't see anything different really except for the size.
Why are A & B a little bit different in size and why is C double the size? I know C could just be double the size but the sticks all have the same unique print on them and look identical (which makes me think they would be identical). I have the feeling that maybe also A and B are 2Gb (1800MB formatted) and somehow I don't see that (and I'm not able to reset that). Also the fact that the larger (C) is about 2 times slower than the smaller ones (A&B) is weird (maybe).
Suggestions? Are there tools that reset all (wiping is OK) or that read the real capacity?

[John Gray]

Perhaps have a look through one of the collections of USB utilities, like this one from OlderGeeks.

USB Disk Storage Format Tool and USB Repair (for example) might be worth a look?

There is also an old HP utility (HP USB Disk Storage Format Tool) which completely clears a USB Flash Drive, which you can find at the website of your choice.

[ErikJan]

Thanks John, already looked @ OlderGeeks. Couldn't find anything there.
Wiping/clearing is no a problem, question is what is cleared: if a tool reads the wrong capacity...