$base: .25;
 $size-map: (
  6: ru(.25),
  12: ru(.5),
  18: ru(.75),
  24: ru(1),
  36: ru(1.5),
  60: ru(2.5),
  84: ru(3.5),
  120: ru(5),
  162: ru(6.75),
 );

/** -- shared spacer util classes --
  Common spacer sizing incrementing ru(.25) to ru(2.5)
*/
@for $i from 1 through 10 {
  .top-#{$i} { margin-top: ru($base * $i); }
  .bot-#{$i} { margin-bottom: ru($base * $i); }
}

.top-0 { margin-top: 0; }
.bot-0 { margin-bottom: 0; }

.top-11 { margin-top: ru(3); }
.bot-11 { margin-bottom: ru(3); }

.top-12 { margin-top: ru(6); }
.bot-12 { margin-bottom: ru(6); }

@each $type, $size in $size-map {
  .size-#{$type} {
    margin-top: $size;
  }
}