How do you interpret the polynomial equation for the volume of a 3-D Washer?

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Can anyone explain what's going on in this formula for me?

Formulas: [ (x^2 + y^2 ) > r1^2 ] , [ (x^2 + y^2 ) < r0^2 ] , [ z^2 < (h0/2)^2 ]

Formulas with constants filled in: [ (x^2 + y^2 ) > 2^2 ] , [ (x^2 + y^2 ) < 10^2 ] , [ z^2 < (2/2)^2 ]

The formulas are supposedly describing the volume of a 3D Washer. I understand the first two terms are describing the volume of the 3D Washer exists between r1 and r0, but I don't understand where the [ z^2 < (h0/2)^2 ] part comes from. Perhaps it is describing the position of the washer in the z-direction, but I don't completely see it.

Any help with interpreting the formulas would be much appreciated.

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In this definition, the first two inequalities describe a cylinder with a smaller cylinder removed and the third inequality specifies the height of the washer.

The third inequality is squared so that the washer is centered around the x-y plane. $z^2 < (h0/2)^2 $ is the same as $|z| < h0/2$ so the total height is $h0$ ($h0/2$ above the x-y plane and $h0/2$ below it.