The bottom bearing on my road bike has seized I took it out and it says on the side 52x12x45 but I can’t seem to find a corresponding size on any websites.

I know I could email a supplier and ask but you get a faster and more accurate response here. IMO.

more accurate response here

Not for headset bearings, there a complete bugger, normal bearing supplier dont tend to stock the type of bearings we need for headsets, that have an angled upper and lower contact surface.
I’d make a wild guess that you need the T808 from this page but as the supplier behind it hasn’t pulled his finger out, getting them from a them or anywhere not from the original manufacturer is a bit problematic.

Sorry, thought I was posting on my headset thread so deleted entry.

The make and model of the headset would help.

Either FSA or Barelli – the finishing kit is Barelli.

Found what I needed here:
Airebearings

http://www.ebay.co.uk/sch/airebearings/m.html?_nkw=&_armrs=1&_from=&_ipg=25&_trksid=p3692