Illinois Size 18s Model 5: Overview & Production

The 18-Size Model 5 was introduced to the market in November 1891 with the new "Bunn Nickel" movement. This model was an upgrade from the Model 2, using an improved train that was more suited for precision timekeeping. The company produced various high-grade movements in the Model 5 while maintaining Model 2 production until c.1895, when the Model 2 was discontinued. Because the Model 2 and Model 5 are similar in design, it is sometimes required to disassemble the movement to distinguish between the two. According to material catalogs published by the company, the 4th wheel on the Model 2 features either 63 or 70 teeth while the 4th wheel on the Model 5 features 80 teeth. Other clues can be used as a guide to distinguish between the two models. For example, all of the Model 5 movements feature a micrometric regulator, either Chalmer's plate-mounted regulator or the balance-cock-mounted regulator that is more prolific in later production. None of the Model 5 movements were fitted with a plain regulator and standard plate-mounted index. If those elements are present, the movement can safely be identified as a Model 2. Also, according to material catalogs, the upper center jewel was not offered for the Model 2. So, if the 18-Size hunting lever-set watch features 16 or more jewels, it can be classified as a Model 5. The only ambiguity is presented when evaluating movements that feature Chalmer's patented micrometric regulator, a design that was utilized on both Model 2 and Model 5 movements. Generally, the earlier Model 5 movements were high-grade, and the finishing can easily disclose the Model 5 design. However, some late Model 2 movements also feature Chalmer's patented regulator, and it is unclear when the transition occurred with these movements. The earliest run of Model 5 movements starts with serial number 1,093,501. Any 18-Size hunting lever-set movement before that serial number is a Model 2. It is also fairly safe to conclude all the 18-Size hunting lever-set movements were transitioned to the Model 5 design by serial number 1,300,000. Between serial numbers 1,093,501 and 1,268,200, it appears that the only grades manufactured in the Model 5 design were Bunn, Bunn Special, 64, and 65. If the movement is classified as one of those grades within this serial range, it is almost certainly a Model 5. Otherwise, it is likely a Model 2. As a result, the more ambiguous range can be shrunk to approximately 1,268,001 to 1,300,000. For those movements, counting the teeth on the 4th wheel is the only method to determine the model.