What This Kit Actually Is
This is a 16-inch stainless bellows flex pipe, sold as a kit — bellows section plus the mounting hardware to get it back in the truck. It's the flex joint, not a straight pipe, so don't confuse it with a rigid exhaust tube when you're pulling the old one for comparison.
Fits Kenworth C500 model years 2007-2015, but Paccar ran a few different exhaust routing configs across those years depending on engine and chassis spec. Length and flange spacing matter here — 16" is the nominal working length of the bellows itself, not counting any pipe stubs welded to it.
Before you order, pull the old bellows and measure flange-to-flange, and check the bolt pattern on both ends. If your old part number matches anything in the cross-reference table, you're in good shape.
How the Cross-Reference Numbers Line Up
M66-7091-0320 is the headline Paccar number, and it shows up under Automann as 820.B75320P and under Paccar Parts as EWPB11861 — same physical part, different catalog systems. Automann repackages a lot of Paccar-spec exhaust flex components under their own numbering, so seeing their number cross isn't unusual.
Watch for one thing on this specific kit: Paccar also lists M66-6541-0320 as an interchange, but that number sometimes shows up on a slightly different flex length or bellows wall thickness depending on the parts catalog revision. If your old part carries that number, don't assume it's identical — check the bellows OD and overall working length against what you're pulling off the truck.
The safest way to confirm fit is by VIN through your Kenworth dealer parts lookup, or by cross-checking the number stamped or tagged on the old bellows unit. Exhaust flex sections take a beating from heat cycling, so numbers can get hard to read — if it's illegible, measure instead of guess.
Ordering Through PartStop
We stock this one in Tacoma and it goes out same-day if you order before our afternoon cutoff — useful when a truck's sitting with a blown bellows and you don't want it idle waiting on freight from a warehouse three states away.
Ship nationwide too, so if you're not local, doesn't matter — we get it moving the same day regardless.
Every flex pipe kit we sell carries our 6+ month warranty. It's an aftermarket part, built to interchange with the OEM number, not a factory reproduction — so confirm fit against your VIN or old part before it goes on the truck, and if something's off, call us before you cut anything.
M667091 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to M667091. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| Automann | 820.B75320P |
| Paccar | M66-7091-0320, M66-6541-0320 |
| Paccar Parts | EWPB11861 |
Frequently asked questions
Does M66-7091-0320 fit my Kenworth C500?
Likely, if it's a 2007-2015 model, but Paccar changed exhaust routing a few times in that range depending on engine spec. Confirm by VIN or by matching the number on your old bellows before you order — don't go off model year alone.
Is this the same as the Automann 820.B75320P?
Yes, that's the Automann catalog number for this same bellows kit — Automann just repackages the Paccar-spec part under their own numbering. Physically it's the same flex section.
Can I just weld in a generic flex pipe instead of matching the exact number?
You can, but you'll be guessing on bellows length, flange spacing, and wall thickness, which matters for how it handles engine movement over time. Cheaper to measure the old part and order the correct cross now than to redo a weld job in six months.
Not sure it fits? We check before you pay.
Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
More cross-reference guides
Need the part, not just the reading?
Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.