Essentially, an OD part fits into an ID (expanded) fitting. OD is a male fitting, and ID is a female (expanded) fitting.

More commonly, we see stacks with reduced to 5" OD (xxxB items) in lengths between 30"-64", which are used in applications for trucks with existing mufflers in place. Also, stacks that are reduced to 5" ID (xxxD) are most often ordered in lengths of 72"-120", and are used in applications where the mufflers have been removed and the stack is installed using the factory elbow, which is more commonly an OD part- though we recommend checking the fittings in both applications.

In cases that do NOT match either description above-

xxxA end form stacks are typically used in our kits. 

xxxC end form stacks are used in cases where the customer has a stack with an OD fitting in the same diameter as the required stack, which does not have a taper-loc fitting, stack will fit over the stack of the same diameter.

Our stack part numbers are all built the same way. Once you understand which digits within the item number designate what, it is easy to build the item number you need. Each stack number consists of 11 digits-

XXXX-XXX-XXXX

The first block of 4 digits dictates the stack style, diameter, and end form.

1-Style (1-Miter, 2-Standard Curve, 3-Bullhorn, 4- Flat Top, 5-Short 30, 6- West Coast Curve, 7-Diablo)

2-N/A- this digit will always be a zero/0.

3-Diameter (5- designates a 5" DIA stack, 6- designates a 6" DIA stack, 7- designates a 7" DIA stack, 8- designates an 8" DIA stack)

4- designates the end form (or, bottom) of the stack. A- OD/straight cut, B- Reduced to 5" OD (typically for muffler applications), C- ID/expanded end form (non-reduced), D- Reduced to 5" ID (expanded-typically work with non-expanded factory elbows)

example: item 107A would be a MITER in 7" DIA, with an OD end form

The second block of 3 digits designates only the height of the stack.

example: 36" stack would be -036-, 44" would be -044-, 96" stack would be -096- and so on

The remaining 4 digits of our part numbers designate the finish of the stack.

On almost all applications, the part number will end in -1103, which designates a finished, chrome-plated carbon steel stack.