Formatting thumb drives

I have several USB2 thumb drives all purchased in recent months.
All FAT 32

#1 has a defunct ISO file on it (copied from a download)
#2 has mixed media (mostly TXT files

I was about to recycle #1 by reformatting it, when I noticed Allocation Unit size:= 16 kilobytes
But #2 has Allocation Unit size:= 4096 bytes

I have never reformatted either #1 nor #2 ... so it leaves me perplexed
Two other thumb-drives purchased at the same time are also 4096 bytes

How might #1 have been changed from default 4096 bytes (4KB) to 16 KB by merely copying the ISO over. ?

What do range of various capacities represent in Formatting drives ?
What would be the best Allocation size be for mixed file types ? (txt, pdf, xls, doc, dll, exe, ini, mp3 ... etc)


Thank you :)

@ jumanji +1

My thumb drives are el-cheapo Sandisk Cruzer 8GB.
- I should have indicated that in the OP

Cannot fathom how thumb-drive #1 (with ISO) is 16 KB on an 8GB device.

According to the table you supplied the 8GB should all be 4 KB (4096 bytes)

Your table is very handy, I'll snip it for future reference.
- better still I just found the table
- I didn't know what to "search" for, default cluster sizes for fat32 did the trick

I presume any of the "Not supported" would have to be NTFS ?

Thank you :)
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Windows7 32-bit Home Premium

@ LMiller7 +1

On one wiki-page ... clusters >4KB are ignored by defraggers. So much for defragging.
I find the nuts and bolts fascinating.

Thank you for leading me out of the dark into the light :)