The shot peening media should be spherical. Broken and uneven particles may produce harmful effects.

The shot peening media should at least have the hardness of the part to be peened, otherwise the compressive residual stress will be significantly reduced.

The shot peening media should be conditioned to have only particle size to the established limits, otherwise the depth of compressive stress layer will be reduced.

The shot peening media should be dry, free from dust and clean, otherwise there will be a damping effect and the compressive residual stress will be reduced as well as the depth of compressive stress layer. Parts also could be unacceptably contaminated.