I am clueless and after spending a couple of hours googling I was convinced I had ordered the correct replacement crankset for my Defy, I ordered: Shimano 105 FC5750 Compact Road Chainset 175mm 50/34T Black from tredz as part of a bigger order.

I have just come to fit them and they are clearly the wrong type as the axle is much bigger in diameter than the ones I removed!

Could you please tell me which ones I need as I am now non the wiser! Thanks

Anyone? More googling and I am still none the wiser!

Sounds as if you have ordered the cranks that fit the press fit BB rather than the cranks for the screw on BB..

Have you got a direct link to what you ordered?

Are you replacing the bottom bracket at the same time?

What cranks & BB do you currently have fitted?

What model Defy is it?

It’s a Giant Defy Composite 3 2012, I ordered this: https://www.tredz.co.uk/.Shimano-105-FC5750-Compact-Road-Chainset_35780.htm

Cranks are the original FSA omega exo and the BB is FSA megaexo pressfit. I am no planning on changing the BB as it was replaced last year.

Thanks for your help

Only an FSA Omega crankset will fit that bottom bracket AFAIK so your options are another one of those or a new bb.

Erm…I think that’s your problem then.

Shimano Hollowtech II use a 24mm axle diameter.

Looking on the FSA website the Omega Megaexo crankset has a 19mm axle diameter:

http://shop.fullspeedahead.com/en/type/cranksets/omega-crankset-3795

Should be easy enough to measure the axle diameters of the two cranksets.
If the crank you are taking out is 19mm axle diameter then your only option if you want to use the new 105 crank is to buy a suitable bottom bracket.