Back in 09, Profile Racing introduced the product that revolutionised all current methods of holding your wheel onto your bicycle. It's the Profile 3/8's Volcano Washer. 
Made in the USA from aluminium, these shapely devices hide those unsightly allen bolt heads and smooth out the look of your dropouts without adding significant weight. A pair weighs 12g (.5oz) Get yours today!

Also included is a steel flat washer that should be used as well, or else the Aluminium will be crushed to bits. You don't want that.

Comes with 2 Aluminium Bolt Head Covers and 2 Steel washers, enough for one hub. (Hub not included.)