iMac 21.5 Core i3 mid 2010 SSD swap, is a bay required

When swapping out the mechanical drive for an SSD in these machines, I've seen people put in a size-up caddy. But is this needed - can I just gaffa tape the drive to the back or something?

Solution 1:

If it never gets moved around, you could actually just leave it loose inside the casing.

It won't make any practical difference, you just don't want to be shaking it around unnecessarily.
I wouldn't think of doing it in a laptop, but a desktop it will be fine.

I had an SSD hanging loose inside the optical bay of a Mac Pro for about 5 years with no ill-effects at all - & in fact I'm not sure that more than one of the Mac Pros here has a proper mount at all, & that one is only because the machine came with it. As soon as I need the bay for another big HD, it will go up in the optical bay like the rest.