It is a special type of brush the top of which are chamfered at a related angle towards the dividing line. Pressure to the brush is applied vide a top piece generally made of insulation material which has a cushioning effect.
Tandem brushes are special pairs of brushes where each pair is considered on a single brush fitted in its own box of tandem brush holder pressed on the commutator body by separate pressure finger. The result is a symmetrical brush pressure and current distribution.
The solid brushes which are generally heavy and rigid are cut into 2/3 or 4 parts of equal sizes for creating better electrical and mechanical contact condition. It leads to a large number of electrical contact point between the brush surface and the commutator. The cutting of the brush causes smaller acceleration and better dynamic properties. It gives satisfactory results mainly on machines which got reversing operations.
When each segment of split brush are bonded together wit resin they are called sandwich brushes. From mechanical point of view, it can be treated as a block brush with additional polishing effect. From electrical point of view, it has an increasing cross resistance which influences the commutation properties of the carbon brush.