Having recently (2014-ish) had a similar question, I have a few references
handy. For a start:

The Truesdale/Erickson list from 1997, focusing on variants of the spiral
ratchet in the model 30 and similar: http://swingleydev.com/ot/get/14128/thread/#14128
">http://swingleydev.com/ot/get/14128/thread/#14128  (in case if broken
link, search for truesdale in the archive)

A discussion from 2014: http://swingleydev.com/ot/get/247930/thread/#247930
A">http://swingleydev.com/ot/get/247930/thread/#247930 A nice summary, with
pictures, of the ratchet spiral types: http://www.oldtoolsnstuff.com/ya
nkeescrewdriverpage.htm">http://www.oldtoolsnstuff.com/yankeescrewdriverpage.htm

A number of technical pieces for a variety of Yankee (and other makes) are on
George's page: http://www.georgesbasement.com/
">http://www.georgesbasement.com/    He leans toward the braces, rather than
the spiral ratchets



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