Westfalia MD 150 Q Instruction Manual page 17

Before mounting, check the grinding wheel for damage visually and
acoustically. Visually check for cracks. After the visual check, gently strike
the wheel with a hard object. The sound must be clear and sounds alike in
all parts of the wheel. If the sound is dull, the wheel is probably cracked
and should not be used.
Do not use a cracked grinding wheel, it is not able to withstand the loads
of use and may suddenly break up during use.
4. Mount the wheel as shown below.
FIG 7
Paper/
Fiber-
Disc
Operation
Flange
Grinding Wheel
Flange
12
Paper/
Fiber-
Disk
Nut