How to Vet Automotive Component Specifications: The 5-Step Verification Checklist I Use at Morimoto

Who This Checklist Is For

If you're an engineer or buyer at an OEM or Tier 1 supplier, and you've ever received a batch of parts where the dimensions were off—or the material grade didn't match what was quoted—this is for you. I've been on both sides: specifying parts and reviewing what comes in. Here's the 5-step checklist I use at Morimoto to catch issues before they hit production.

Look, I'm not saying every supplier is out to cut corners. But I am saying that without a structured verification process, you're relying on trust alone. And trust doesn't hold tolerances.

Step 1: Create a "Spec Brief" Before You Send the RFQ

Here's the thing: most specification errors happen before the order is even placed. The buyer sends a generic drawing, the supplier interprets it their way, and you get something that's close but not right.

What I do now is create a one-page spec brief for every new part number. It condenses the critical tolerances, material grades, and surface finish requirements into a single sheet. Things like: "Material: 6061-T6 aluminum. Tolerance on hole placement: ±0.1 mm. No burrs on internal edges."

I only realized how important this was after ignoring it once and eating a $3,200 redo on a batch of 500 stampings (surprise, surprise). The drawing had all the info—but the supplier's production team never looked past the first page of the PDF. Now the spec brief is part of every RFQ.

Your check: Does your spec brief explicitly state the three most critical features? If you can't name them, chances are the supplier won't either.

Step 2: Verify the Supplier's Inspection Process, Not Just Their Certificate

I've seen certified suppliers ship parts that are out of spec. The certificate says they're ISO 9001. The parts say otherwise.

When I ran a blind test in Q2 2024 with five Tier 2 suppliers (same drawing, same material), the dimensional variation between their first-article inspections was way bigger than I expected—up to 1.2 mm on a critical locating hole. One supplier caught it internally. The other four? They shipped it anyway.

Your check: Ask for their inspection protocol. What gauges are they using? Are they measuring the first part off the tool, or every 100th? Are they using CMM or calipers? The answer tells you everything about their actual capability.

Step 3: Do a "Side-by-Side" on the First Article vs. Your Reference

This step feels obvious, but it's the one people skip when they're in a hurry. When I compared our Q1 and Q2 results side by side—same vendor, different production batches—I finally understood why the details matter so much. The first article looked fine in isolation. But placed next to our reference part, the color match on the anodized aluminum was off by 3 shades. Would a customer notice? Maybe not. But our brand standard says no variations.

Don't just check dimensions. Check surface finish, edge condition, color, and feel. The tactile difference between a stamped edge and a laser-cut edge is obvious when you hold them together.

Your check: Keep a master reference part locked in a cabinet. Physically compare every new batch against it. Not a digital file. The physical part.

Step 4: Run a Mini-Production Run Before Full Commitment

I'm a fan of efficient processes—honestly, I believe reducing manual handling also reduces error rates. But I learned the hard way that testing a single sample isn't enough. The first article might be perfect. Part #47 might be the one with the burr.

For our 50,000-unit annual order on the Morimoto LED tail light housing, we now request a 50-piece pilot run before we authorize full production. It's an extra step. It adds about 3 days to the timeline. But that pilot caught a die wear issue in 2023 that would have affected 8,000 units. The cost of the pilot: $1,200. The cost of reworking 8,000 units: $22,000 (which, honestly, felt excessive).

Your check: Build pilot runs into your contract. If the supplier resists, ask why. A confident supplier welcomes the verification. A corner-cutter will push back.

Step 5: Document Every Deviation—and the Resolution

Between you and me, this is the step that saved us the most headache over the long haul. In 2022, a vendor sent a batch of drive shaft components where the thread depth was off by 2 mm. The part was technically functional, but it didn't match our spec. We rejected it.

But here's the thing: a year later, the same issue came up with a different supplier. Because I had documented the first deviation—including the root cause (a worn tap) and the corrective action (regular tap replacement schedule)—we identified and fixed it immediately.

Your check: Keep a simple log. Part number, date, deviation, root cause, resolution. It's not just for quality audits. It's a knowledge base that helps you spot patterns. And if you ever need to switch suppliers, that log is gold.

Final Thoughts: The Cost of Skipping Steps

I went back and forth on whether to include a "shortcut" version of this checklist for rush orders. Ultimately decided: don't. Because the one time you skip a step is the time a bad part gets through. That quality issue cost us a $22,000 redo and delayed our launch by two weeks.

Looking back, I should have insisted on this process from day one. At the time, I didn't want to slow things down. But the efficiency you gain by avoiding redos is way more valuable than the few hours you "save" by skipping verification.

Bottom line: Use this checklist, adapt it to your parts, and save yourself the expensive lessons I already learned.