1990-2005 Mazda Miata Rain Rail

A rain rail is a U-shaped, molded ABS plastic piece that attaches to the rear bottom of the convertible top.  It directs any water collected out drain holes to keep it from entering your interior cabin and trunk. 
Unless your top is leaking, you probably do not "need" a new rain rail, however, there are good reasons you should consider getting one anyway if your are replacing your convertible top.

There is a significant amount of time and labor involved to drill out the old rain rail and reinstall it on a new top properly - without any wrinkles.  If you are doing it yourself, and are sure your existing rain rail is in good shape then you can save some money by purchasing a new top without the rain rail. But, if you are using a professional installer, the amount of additional labor they will charge to do this work will likely offset any savings you have from not buying a new rain rail already installed.

If you order a new convertible top with a rain rail, it will already be attached at the factory making the installation much easier. 

This unattached rain rail is a perfect replacement for your old plastic rain rail and comes separately in its own box.