Spacers are necessary if you are making a rimmed piece. They elevate the piece slighty above the drying surface to prevent rim from slumping in the kiln during firing.
The spacers are sold in 1/2 inch thick pieces and 3 inch x 3 inch dimensions. They can be used for all forms big or small.
Place under under the center of the form by lifting the finished piece and placing it back down on the spacer. To see tutorial images of Grand Rapids Pottery using the spacer, check them out the GR Pottery Forms website here.