Bob is spot-on about #3 ... these knurled thumb-nuts are quite common, outside of the residentially ubiquitous adjustment knobs for clock hands, perhaps most common in making terminations of wires carrying a low-voltage DC electric current on a projecting screw (post). Many early commercial batteries (especially the batteries used for telephones) had precisely this type of terminal for making connections. They were also quite common for making the connections to meters (ohmmeters, ammeters, voltmeters ... such as those used to monitor the condition of batteries) and (perhaps a few years later than your dates) for making connections to the backs of the meters in automotive dashboards. You can see an example of a contemporary voltmeter with this type of terminal here (though the thumbnut is missing on this example, you can clearly see the post where it is supposed to be screwed-on):

http://i15.ebayimg.com/07/i/000/a9/94/7bb9_1.JPG

There is another example here (with the thumb-nuts intact):

http://cgi.ebay.com/W-M-Welch-Vintage-DC-Volt-Amp-Meter_W0QQitemZ190130744466QQihZ009QQcategoryZ50963QQrdZ1QQcmdZViewItem

These were also a quite common termination type on early battery-powered radio sets (you can see a bunch of examples on this very early single-tube radio):

http://cgi.ebay.com/Antique-Battery-Powered-TUBE-RADIO-Stein-MICA-1900s_W0QQitemZ120140885094QQihZ002QQcategoryZ12QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

After WWI, the knurled thumb-nuts used for electrical applications commonly had an exterior surface of bakelite over the brass core (for its insulation protection against inadvertent shorts), like the examples seen here on a common AC/DC power supply used to power the old-style battery-powered radios from household AC current:

http://members.aol.com/delamewes/batelim1.jpg



From:         "Robert C. Leavitt" <[log in to unmask]>

Doug:  I'll take the obvious.

#3, especially center and right, are knurled thumb screws, used for 
any number of applications where you want a fairly firm hold but 
didn't want to use a tool: electrical connections like for installing 
a battery pack; fastening the cover onto a box (some cars used them 
to fasten the cover on the fuse box, for example);  also used for the 
time-set  adjustment on a wind-up alarm clock.  The center one 
screwed onto a threaded post and would restrict the degree to which 
it could be tightened.  The right one screwed into a threaded hole.




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"There is also an artificial aristocracy founded on wealth and birth, without either virtue or talents ... The artificial aristocracy is a mischievous ingredient in government, and provisions should be made to prevent its ascendancy."

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