The fitting brackets that come with your RoofBunk should be able to fit roof bars and roof racks with bars as thick/tall as 5cm and as wide as 12cm for the Roamer and 10cm for the Explorer, so any roof bars under this under this should work great! In the rare circumstances that your bars are thicker/taller than 5cm, then we'll be happy to recommend some inexpensive 8cm M8 screws to you, so you can install it. Plus, if you need wider brackets for the Explorer, then you could order the Roamer brackets separately on our shop, as both are compatible with each other! You'll also need to make sure your roof bars/roof rack is rated to hold at least 65kg of weight for the Roamer and 50kg for the Explorer. The reason this may be a lower number than you might expect is because the manufacturers list the dynamic holding weight limit (moving), rather than the static holding weight limit (stationary/still), which affects how much weight they can hold. To give you a rough idea, the static holding weight limits for most of them are around 5-8 times what the dynamic holding weight limits are (depending on the speed, wind and other forces acting on the roof tent when it's moving). So in this case, roof bars with a weight limit of 65kg should be able to hold at least 350kg worth of weight! We suggest getting roof bars that are ideally through bars in design too, as these allow more overhang on the sides and the RoofBunks sit more flush on them. If you're struggling to know where to start finding your roof bars or a roof rack, we recommend using Halfords and entering your reg number plate to help you find the right ones for your particular vehicle. You'll also need to check your vehicle’s maximum roof load capacity is over 65kg for the Roamer and 50kg for the Explorer (even though the vast majority of vehicles are), which can be found in your vehicle’s user manual or after searching for the information online. We recommend checking this Online Vehicle User Manual Directory If all this sounds daunting, then please email over your vehicle's reg plate and we'll do the research for you!