I get .07 cuft per brace //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
edit -oops you asked how //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
17 x 12 x .75 = 153 /1728 = 0.08cuft if the brace was solid
3 x 3 x .75 = 6.75 * 4 = 27 /1728 = 0.01cuft holes in the brace
so
0.08 - 0.01 = 0.07cuft //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif