Works with old style round Yakima bars and with the old Thule square bars.
A great way to quickly outfit your rack for your kayak. These foam "saddles" cradle and protect your kayak, on your rack, or in storage. It is always best to support your kayak underneath the bulkheads (if you have them).
Sold as a pair
16" works well for most single kayaks. 
21.5" works well for wider singles, or tandems.