Mounted on a Straight Tramway handle for safety and durability At the same time, press on the brush to increase pressure. Our Brush Seaters come in 5 grades: ES EX tra Soft, FH Fine Hard, MS Medium Soft-our most popular, FS Fine Soft, and MH Medium HardBrush Seaters are used to easily and accurately seat commutator and slip ring brushes of any material.. 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.