There are 19 styles in the Westclox Big Ben Alarm Clock Style Series
Ring on top, two front legs, three screws through the front of the bezel.
1909 - 1918
Ring on top, two legs in front, no screws through the front of the bezel.
1918 - 1935 (and a reproduction was made in 1970)
Thin edge around base, has steady-repeat and alarm-silent levers on top of case.
1927 - 1932
Concave curves on base (curves on front, rear and the sides).
1931 - 1934
The base has two convex curves (one on each side).
1934 - 1939
Streamlined round case, rectangular base with polished brass or nickel plated inlaid plate. Looks like a Honeywell "round" thermostat mounted on a base. Numeral "12" partially cut away to make room for the alarm dial.
1939 - 1949
Smaller base than style 5, without the polished metal plate. Small alarm hand at "12" with full numeral 12 showing.
1949 - 1956
Concentric alarm hand, plastic lens.
1956 - 1964
Large plastic lens, alarm on-off control on top of case, says "Clock of Tomorrow" on the dial.
1955 - 1959
Oval metal bezel.
1964 - 1981
"Squared" oval plastic bezel
1979 - 2000
Made in China, sweep second hand, top alarm shutoff, rotating alarm dial visible below the numeral "12".
Starting in 2001
Black Bakelite® case, nickel ball feet
1931 - 1934
Metal dial, mahogany case with light color wood strip inlay around front.
1931 - 1935
Brown rectangular Bakelite® case.
1948 - 1952
Rectangular plastic case, digital display.
1974 - 1978
Plastic case with rectangular rounded-corner plastic pedestal base, plastic lens is flush with front of case. Analog or LED display.
1976 - 1980+
Looks like style 8 on a pedestal. Oval clock on tall pedestal with round base.
1975 - 1979
Spherical plastic case with flat bottom
1973 - 1981