Found these in an old book (online):
VOL II The stone age in North America; an archæological encyclopedia of the implements, ornaments, weapons, utensils, etc., of the prehistoric tribes of North America (1910) Author: Moorehead, Warren King, 1866-1939
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There's no scale but in another book I have (The Archaeology of New York State - Revised Edition, William A. Ritchie, 1980) the average length of similar slate points is 3".