The Centennial is any J frame enclosed hammer revolver produced since 1952 when the original 40 (steel frame) and 42 (airweight) were introduced. They were called the Centennial because they were introduced in the 100th year of S&W being in business. These original two models were produced until 1974 when production ended due to low sales.

In 1989 S&W introduced the 640 in stainless in .38Spl. The first year or so had a CEN prefix in the serial number. S&W started the 3 letter/4 number serial numbers in the early '80s. The prefix CEN came normally in the year 2000 timeframe, but in 1989 I guess Smith thought it would be cool to use it on the reintroduced Centennial, hence CEN. This prefix was stopped sometime in '90/'91 I believe. All the CEN prefixed 640s were marked TESTED FOR +P+ in the bottom of the cylinder window. That was also stopped when the CEN prefixes stopped. Btw...at that time S&W just started using then current serial number prefixes which were in the Bxx range.

Later on in '96 the original 640 was chambered in .357MAG becoming the 640-1 and all manner of other models in different calibers and frame materials were produced since then.

Here are some pics of some Centennials I own/owned over the years. There are more, I just don't have pics of them. The 640 no dash is one of, if not my most, favorite S&W revolver ever. Mine is an early one, CEN0xxx.