C&C Bought cubes for making cage, just wanted to check they're ok

It's measured across the opening, straight across between the bars.

Good good. I was kinda worried at first that it was 1.7 inches, then I realised that was including the bars on either side.

I'ma start working on it monday or tuesday, whenever the furniture currently occupying the space it will be in goes out to the kerb.

How many spaces are there and what size (in inches) is the grid?

There are 9 spaces each way (so 81, if my maths doesn't fail me) and the grid is just under 14 inches each way.

That's what mine are and I'm sure that mine are fine, my boys can only stick their noses through.

yup that's the size that is suggested.

This is what mine is as well.
I don't know how young your Guinea pig is, but if he/she/they are very young you will HAVE to baby proof, Mine is almost 4weeks old and literally just jumped right through my grids, her little hips got caught just a little but her c&c cage became baby proofed and no problems now. Their are a few different ways to do this.

She's just under a year old, so she'd have to pull some kind of miracle to shrink and get through I think.