Musser Moto-Carts For Mallet Instruments Bring A New Dimension To Mallet Percussion Design With Durability For The School Band And Drum Corps. The Black Finished 2" Square Steel Adjustable Frame, Rolls Smoothlly On 6" Swivel Casters Over Grass, Dirt, And Cement. These Rugged Retro-Fittable Frames Are Perfect For 'Pit' Percussion On The Field. If They Hold Up On The Field, You Know They'Re Great For The Concert Hall.