Parts numbers, we've all seen them. While most of us know they mean something, we don't know just what the part number can tell us. By now, folks who use these codes to identify parts for their Cougars have figured out that the first two digits of a part number identify the model year the part was designed for, but beyond that the rest is just a meaningless jumble. That means you have to take the word of a parts seller when he says, "Sure it will fit your car," but you won't know for sure until you get home and try to install the part. Or, you can take a little time to understand what those digits can tell you and know you have the right part before you lay down your hard-earned money.

Part numbers break down into three sections, normally separated by dashes. The first section is always four digits. The second section is normally four or five digits but can be as much as 7 digits. The last section is normally one digit, although it can be as long as three digits.

Let's use the number on the part pictured below as an example to see just what it can tell us. The part is a starter relay--something you see every time you lift the hood on your Cougar.

To the best of our knowledge, this is the original starter relay installed on our 1969 Cougar XR-7.

TCCN File Photo

The first character is always a letter and identifies the decade in which the part was designed. The decade codes begin with the letter A, which represents the 1940s. The chart below shows that the letter C on our starter relay indicates that it was designed in the 1960s.

The second character is always a number and stands for a year within the decade. For example, a 0 indicates the first year in the decade, 1 stands for the second year in the decade, and so forth. In our starter relay example, C7 translates to the part being designed in 1967.

The third digit in the first section of a part number--usually a letter--represents the type vehicle the part was first designed for and is called the Product Line Code. It is important to note that the part may be found in vehicles other than the one indicated by the Product Line Code. In our example the A indicates that, even though the relay is found on a Cougar, the part was originally designed for use in Full sized Fords.

While the Product Line table below lists some of the Product Line Codes, F/L/M has produced a lot of vehicles, so some of these codes have been reused over the years. For example, at different times, the letter "D" has indicated Falcon, Maverick, Grenada, midsize LTD, and Taurus. F/L/M recently started using numbers in the Product Line Codes, but for everything that fits our Cougars, this code will be a letter. What makes this digit special is when a part is unique to a particular vehicle. So, when someone says those NOS leaf springs are for a 1968 Cougar and the third digit is not a "W", they are not Cougar leaf springs. First and second generation Cougar rear leaf springs are unique to Cougars--they were designed for and only fit Cougars.

The last digit in the first section of part codes--also a letter--represents what division within F/L/M was responsible for coming up with the part. This digit can tell you what section of the car the part was designed for. It can also indicate whether the part is original, a service replacement part, and for some very rare parts, factory performance parts. Our example part number has an F division code, which our chart translates to "general parts."

The next section of the part number indicates what the part is. Normally four digits, the base part number can be expanded to as many as seven digits depending on the part. The part number is first broken down by series, then further subdivided for parts within the series. For example, our starter relay has a base part number of 11450, which means that it is a component in the starting system. The "450" identifies a particular part, the starter relay in this case. The part number code can expand to seven digits when referring to certain interior and trim parts that are specific to a body-style."

The following table seems to be the closest list part number series codes I've found for our generation of vehicles. There are other lists out there on the net, but like the Product Line Codes, the numbers have morphed over the years to mean different things.

5200 EXHAUSTS
5300-5400 FRONT SUSPENSION
5500-5900 REAR SUSPENSION

SAFETY EQUIPMENT (JACKS, SPEEDOMETERS, WINDSHIELD WASHERS & WIPERS, MIRRORS, BUMPERS)

The last part of the part number is the suffix. The first digit usually matches the Product Line code as it indicates that the part was made for a specific product line. The second digit, if there is one, indicates the change level. In our example, the starter relay design had been modified once from the original design. If there are three digits here, its meaning changes. The body-style specific parts mentioned earlier are usually the only ones that used three digits, which usually indicate the color code of the part.

A WORD ABOUT CASTING NUMBERS

While we've been talking about part numbers here, this information also applies to most casting numbers, but F/L/M threw a wrench in the works with casting numbers. Most casting numbers are the same as the part number, except with cylinder heads. So, for cylinder heads, a C5OE head may be identical to a C8OE head. While I've only seen this happen with cylinder heads, F/L/M may have also pulled this trick with some other parts too.

In an attempt to give credit where credit is due, I referenced the following resources when researching this article. Due to the duplication of information in various sources, some of the references are included because they confirmed the information found in another resource.

• "Breaking the Code. Taking the Mystery out of Ford Part Numbers" by Jerry Heasley (published in the January, 1989 issue of Fabulous Mustangs and Exotic Fords magazine)
• "1960-1970 Ford & Mercury Muscle Parts Identifier" by Warne Robert Products (published in 1997)
• "Ford Parts Interchange Manual" by Paul A. Herd
• http://www.classicmustang.com/casting_numbers.htm
• http://www.fairlanet.com/partnumbers/