Listen to the sound of bars of different thicknesses by hitting them!
What kind of connection can you find between the thickness of the bar and the pitch of the given sound?

A thicker bar gives a higher sound and, accordingly, the oscillation frequency is higher because a bar which is thicker in the direction of the oscillation is stronger and behaves more elastically against deformation.

The elasticity of a bar depends on its material, for instance in the case of an aluminium and a steel bar of the same shape, the steel bar gives a higher and longer lasting sound. A bar made of wood gives an even deeper, duller, and shorter lasting sound.