Pitch spacers are made of molded plastic and provide the desired pitch toward the drainage side of the deck ceiling. By adding 1 additional spacer per joist you increase height or slope. These fasten to the joists with stainless steel screws. 32 per bag. 2" W. x 1/2" H. x 2-1/2" L. To figure number of parts for deck, go to www.drysnap.com and click on calculator.