Bike racks and roof bars etc

Hi all. Hoping someone can help me with this.

After 7 years I've finally bought a new car - but have now discovered that none of the stuff I have for the old one fits so I'm in the process of changing it all. Part of the problem is that I bought most of it over 10 years ago and my last car had the same sort of bars so it's all a bit old now. We've got a roofbox and 4 bike racks that go on the roof. I'm going to get a towbar fitted so that I can put a bike rack on the back instead - dog takes up the rear when we go away now. I got a towbar mounted rack for free locally that will do for now.

My roof bars are different so I need to get new ones - and I want to be able to fit my current stuff on them. The current ones are square and most of the new ones I see are aero/oval. That part is easy - I'll just get a set with compatible feet. The part I can't work out is how you attach a roofbox to them.

The one I have has metal brackets that go around the bars and then have knobs you tighten them with inside - they're sort of u-shaped but with fairly right angled corners like this:

https://i.ibb.co/J5d5BBx/Screenshot-...1-17-00-51.png

For fitting to aero bars do those work?

Or they all seem to have t-track bolts you can get - do you just put a single bolt through the bottom of the box with a big washer? That's as secure as this thing with 2 bolts?

Nothing I can find seems to give me a definitive answer so I'd be grateful if someone's done it and can tell me how.

Thanks.

Typical - 2 minutes later Amazon sends me this - fixings for an aero rack:

https://i.ibb.co/mC3hxLX/Screenshot-...1-17-10-23.png

Besides being a bit scary how it knew that that looks like the answer - unless the t-track things are better/stronger?

Look to the brand that makes your roof box or the brand that makes your cross bars. I know that Yakima (aero) makes mounting brackets to switch some Thule (square) attachments to their system and vice versa. You may have to call them if it doesn’t show up on their websites. I think the boxes are especially likely to need adapters, because box manufacturers sell boxes to fit on car manufacturer installed cross bars and so also make adapter brackets to fit those bars.