Here's a crude Persistence of Vision definition for a  Happ Controls part number 58-9100-L:
#local Button = object { //Bottom of outer ring is Y = 0
   union {
      difference {
         union {
            torus {1.3/2 - .16, .16 sturm}
            cylinder {<0, 0, 0> <0, .16, 0> 1.3/2 - .16}
         } //union
         cylinder {<0, .01, 0> <0, .2, 0> .9/2}
         box {<-1, -1, -1> <1, 0, 1>}
      } //difference
      difference {
         union {
            torus {.87/2 - .1, .1 sturm}
            cylinder {<0, 0, 0> <0, .1, 0> .87/2 - .1}
            cylinder {<0, -.3, 0> <0, 0, 0> .87/2}
         } //union
         sphere {<0, .83, 0> .8} //Depression
         translate .22 * y
      } //difference
      cylinder {<0, .001, 0> <0, -2.47, 0> 1.1/2}
   } //union
   texture {pigment {color <170/255, 57/255, 39/255>} finish {reflection .1 phong .4 phong_size 60}}
} //object
The measurements are inches.
This is the definition I used to make the little purple button over there <---