Hi:
Taken from The Beekeeper's Handbook 3rd edition by Sammataro and Avitabile,
1998 :
" A Snelgrove or screen board, sometimes called a division board, is a
double-screened, rimmed, inner cover-size board that has a small entrance on
one side of the rim. It is used to make an increase, to split a colony, or
to start a two-queen colony. The screen separates the queen and the bees in
the lower part of a hive from the queen cells or new queen and bees placed
above; the smaller colony above can take advantage of the heat generated
from the colony below."...
Hope this is of some help.
Keith