. To use the Brush Seater, hold close to the brush so that Brush Seater material will be carried under the brush. Brush Seater, 4-3/4 in X 1/2 in X 1/2 in, Grade Ms For cleaning commutator pick a stone about 3/4 the length of the commutator bar and as thick as will neatly fit between the brushing rigs.