The Designer gravity Grille requires a minimum pressure to open:
   100mm 20Pa
   125mm 30Pa
   150mm 30Pa
Prevents back draughts and water penetration.

Standard Gravity Grille - White - DCT0066, Terracotta - DCT0065, Grey DCT0061
  100mm - Face size 140mm x 140mm, spigot diameter 100mm, spigot length 35mm, cut-out size 105mm
  125mm - Face size 162mm x 162mm, spigot diameter 122mm, spigot length 25mm, cut-out size 127mm
  150mm - Face size 174mm x 174mm, spigot diameter 174mm, spigot length 32mm, cut-out size 157mm

Designer Gravity Grille - stainless steel 304 grade - DCT2147
  100mm - Face size 150mm x 150mm, spigot diameter  97mm, spigot length 52mm, cut-out size 115mm
  125mm - Face size 180mm x 180mm, spigot diameter 120mm, spigot length 52mm, cut-out size 140mm
  150mm - Face size 180mm x 180mm, spigot diameter 145mm, spigot length 62mm, cut-out size 160mm