My IMac (2005) decided to recently pack up but I retrieved the Hard Drive from it.
It is a Serial ATA (so it says) and so I bought a HDD enclosure to retrieve the data. The external enclosure is also a Serial ATA connection but the connections don’t fit.
Can anyone tell me why this is before I go buying and returning many different enclosures?
the reason is, you have an internal SATA drive & you probably bought an external SATA enclosure (eSATA)
Wikipedia
as of 2007, an eSATA external drive enclosure will typically ship with a passive eSATA-to-SATA bracket/cable-adapter to install on desktops that lack an eSATA port or that need another.
this means you need an adapter like this & i think this will do