common.colbox_stair = { --Stairs nodebox
   type = 'fixed',
   fixed = {
      {-.5, -.5, -.5, .5, 0, .5},
      {-.5, 0, 0, .5, .5, .5},
   }}

common.colbox_1_5_slab = { --1/5th height slab
   type = 'fixed',
   fixed = {
      {-0.5, -0.5, -0.5, 0.5, -0.3, 0.5},
   }}