Here are some photos of the brushes installed on my DC FB1-4001A series wound motor, rated at 72-144 VDC, (19kW) 25HP continuous ( 100 ft/lb of torque / 48hp @ 500 amps ) which is   9.1″ in diameter.

My motor has a curved protective metal sheet that wraps around the front of the motor (the aluminum with diamond cutouts that has a cutout for the A2 post in this photo). It has a spring catch that releases it (not shown) on the other side of the motor.

I use the metal sheet to hold down fiberglass screen material underneath the diamond cutouts to provide extra protection from road debris. The brushes are accessed after removing the sheet.

The brushes are mounted in pairs, and each brush is held against the commutator by a metal spring and has two copper pigtails to transfer the current.

Here is a closeup of two brushes where you can see the commutator which rotates under them.