There is a number of ways that roof mounted accessories (bike carriers, roof boxes, water sports carriers, ski/snowboard carriers, etc) can be attached to the bars, depending on the type of bar that the item is being attached to.
Most new roof mounted accessories can be attached to either steel bars, or aluminium aero bars and all the required fittings are provided. It is often normally possible to purchase t-track adapters separately if these aren't supplied with the product (more details below).
T-track adapters
T-track adapters are a T headed bolt that usually sides into a channel on the top of the roof bar. Sometimes the T-bolt pushes in from the top of the bar and twists/expands into place. This allows use of the full length of the bar, so is the best option if you need to carry a lot of, or large items on your roof.
T-Track bolts are only suitable for aluminium bars.
U-bolts
U-bolts fit underneath the bar and are usually secured inside with wing-nuts. U-bolt fittings will be a specific width. You do need to be sure they are wide enough to work with your roof bars. T-track fittings are often available as an option if U-bolt fittings are too wide for your aluminium T-track bars.
Claw fittings
Many of our most popular roof boxes are supplied with claw type fittings. Claw fittings are very easy to use; you just turn a large knob inside the box to secure the fittings to your roof bars. Claw fittings fit most of the roof bars we sell.
Yakima fittings
Many Yakima products have fittings that fit around the bars. These fittings work with most roof bars. T-slot (T-track) adapters are available for a limited number of Yakima products. T-slot fittings will be listed separately, where available.