On the other hand, some of the variations are significant, even now.  The initial patent may have been for a design that was difficult to machine; or awkward to use; or quickly wore out.  The second patent introduced a new way that not only avoided interference with the first patent, but also produced a better article of commerce.  Never mind that the mechanism's basic operation was the same.  My best guess is that there were so many unpatented mechanisms in common use (in the public domain) that if the concept was unpatentable, the execution was.  Witness the little rail road car wheel that keeps the bevel gears of a No.2 Millers Falls eggbeater drill in near-perfect mesh on the pitch lines of the mating gears.  No one ever found a better way; yet the only patent which illustrates this mechanism (that I have been able to find) uses an instantly recognizable rendition of that model as an example of the quintessential geared bit driver: George L. Wilcox, Locking Device for Hand Drills, US Patent No. 1,083,784, January 6, 1914 - It is understood that the hand drill so far described is of the standard type of drill now generally in use. Mr. Wilcox's witnesses were Theo. G. Hoster and Philip D. Rollhaus.

Sometimes it's difficult to imagine the circumstances under which such tools as these were used.  The image, Uncle Mark, gives a hint.

Some of the firms making braces had complex histories.  I have tried to tie some of them together by examining the patent papers, using the working assumption that the attorneys who handled the patent applications must have avoided conflicts of interest by working for only one firm at a time in a given field.  Thomas Earle, Attorney, [see Note 2] and Wilhelm & Bonner, Attorneys, [see Note 1] were two such commonalities.

Ronald W. Pearson, D.O., wrote the definitive book on patented braces: The American Patented Brace 1829-1924 (Astragal Press, Mendham, NJ, 1994)
and he maintains at the Mid-West Tool Collectors Association website a current database on the patents, covering the periods:

The database is also indexed alphabetically by patentee:

Note: Until this study is more complete, you can see the brace images by copying the unlinked file name of a brace (in the column at left in the table below) and then pasting it onto the end of this URL: http://www.georgesbasement.com/braces/