Construction sheet for the 1960 (current 50-star) <a href="https://en.wikipedia.org/wiki/Flag_of_the_United_States" class="extiw" title="w:Flag of the United States">Flag of the United States</a>.  This is apparently the specification published in conjunction with <a href="https://en.wikisource.org/wiki/Executive_Order_10834" class="extiw" title="s:Executive Order 10834">s:Executive Order 10834</a>, which defined the flag.
U.S. Government
1959
From the <a rel="nofollow" class="external text" href="http://uscode.house.gov/download/downloadPDF.shtml">2004 PDF version of the 2004 U.S. Code</a>, Title 4 (direct PDF URL <a rel="nofollow" class="external autonumber" href="http://uscode.house.gov/pdf/2004/2004usc04.pdf">[1]</a>). This is printed there alongside Executive Order 10834, which defined the flag, so presumably this is the attachment mentioned in the order.