Williams
Models and s/n	Y	M	D	Remarks	Ref.
No. 1
	1891			Curved keyboard, 3 row, decorated frame, paper feed roll behind the platen	4
my personal guess: up to 5.000	later			Straight keyboard, 3 row, paper feed roll behind the platen	4
No. 2
my personal guess: 5.000 to 20.000	1897			Straight keyboard, 3 row, paper feed roll behind the platen	4
No. 3
my personal guess: 3 series have probably s/n of their own, starting at 1 again	1897			Model 2 with large carriage (probably Model 1 based as well, according to Reference :5)	4
No. 4
my personal guess: over 20.000	1900			4 key rows, paper feed roll in front of the platen	4
				Models with only capital letters for telegraph offices reported	5
Williams junior 3
	1904			Model 2 with paperfeed roll in front of the carriage, but 3 row keyboard and with large carriage	4
No. 5
	1904			4 key rows, 48 keys, paper feed roll in front of the platen	4
No. 6
	1904			4 key rows, 48 keys, paper feed roll in front of the platen	4
	1909			production of all Williams machines ended	4