Genuine Part or Costly Lesson? A Quality Inspector's 7-Step Checklist for Linear Motion Components

A lot of my job is rejecting things that look fine. I'm a quality/compliance manager at a motion control distributor—I review every incoming batch before it reaches customers, roughly 200 SKUs per quarter. In 2025, I've rejected about 12% of first deliveries due to spec mismatches, unreadable markings, and inconsistent sourcing. Not because parts arrive visibly destroyed. It's the small stuff: a 28BYJ-48 stepper motor with coil resistance reading wrong, a ball bearing wheel that doesn't actually spin free, an actuator label that's just slightly off.

This checklist is for engineers and buyers who source linear motion components and want to catch these problems before they become field failures. Seven steps, about 20 minutes per product family. Most people skip steps 3 and 6. Don't be most people.

When to Use This Checklist

Use this whenever you're evaluating a new supplier, receiving first articles, or getting a batch from a vendor you haven't audited recently. It also works if you're buying from a distributor you've used for years—brands change their product lines, distributors switch import sources, and "it's basically the same as last time" is a sentence that should make you nervous.

Here's what it covers: verifying the official source, vetting distributor claims, inspecting physical markings, measuring key specs, testing batch consistency, checking the parts everyone assumes are fine, and documenting what you find.

Step 1: Confirm the Manufacturer's Official Website

Start here. For Thomson products—people search both "thomson linear" and "thomson-linear"—the official site is the one listed in the manufacturer's own datasheets, press releases, and corporate filings. Search "thomson linear official website" and you'll get plenty of results, but not all of them are official. The real domain should be clearly referenced in the product documentation you already trust. Check the contact page too. If it uses a free email domain or lists an address that doesn't match the company's announced locations, that's a red flag.

I should add that a lot of "official-looking" sites are storefronts that registered a domain containing the brand name. That doesn't automatically make them fake. But it does mean they're not the OEM, so their specs, warranty claims, and distributor locator don't carry the manufacturer's authority.

What to check on the official site:

• Product pages match the part numbers you're ordering
• The download library has current datasheets (check the revision date)
• A distributor locator or authorized channel list is present and working

The verification shouldn't take ten minutes. If it does, something is off.

Step 2: Verify Distributor Authorization

A search for "thomson linear actuator distributor" returns plenty of candidates. Anyone can register an online store and claim to be one. A legitimate distributor, though, can show you a current distributor agreement or a letter of authorization from the manufacturer. Ask for it before you place the order, not after a problem appears.

The question everyone asks is "what's your best price?" The question they should ask is "can you show me your distributor agreement?" Because an unauthorized listing is often 15-30% cheaper. That discount isn't a gift. It's a risk transfer.

People think unauthorized vendors are cheaper because they have lower overhead. Actually, the mechanism is that they buy surplus, overstock, or counterfeit product and shift the liability to you. Per FTC guidelines (ftc.gov), advertising claims have to be truthful, and misrepresenting a product's origin is enforceable action territory. But enforcement takes time. You need verification at the point of purchase.

Here's the total cost angle: the $480 actuator that saves you $120 over the authorized channel can cost you $1,800 in engineering time, downtime, and replacement if it fails. I've lived that. One quality issue we caught late, after it had shipped, cost us a $22,000 redo and delayed our launch by three weeks. The cheapest quote isn't the cheapest part.

Step 3: Inspect Markings, Labels, and Packaging

This is the step engineers skip because it feels like packaging stuff rather than engineering. It matters more than you'd think.

Genuine Thomson linear bearings carry a laser-etched batch code on the housing. A genuine 28BYJ-48 stepper motor has consistent coil color coding, a printed top cover with the model and gear ratio, and driver chip markings that match the datasheet.

Last year we caught a batch of six "identical" stepper motors from the same listing. Three had the original marking. Three were re-stamped. We only caught it because we check markings every single time. It takes four minutes.

Don't fully trust holograms or void tape either. Some are faked. But their complete absence is a strong signal, so note that in your records.

Step 4: Measure Critical Specs on Arrival

The datasheet is an advertisement. The measurement is the truth.

For a 28BYJ-48 stepper motor, that means:

• Rated voltage: 5V DC, unipolar, 4-phase (check your exact variant)
• Coil resistance: typically 20-60 ohms per phase depending on the version
• Step angle: 11.25 degrees per step with the 1:64 gearbox

Measure each coil. If one reads open or shorted, reject the batch. But also record the values — scatter across the batch tells you something about manufacturing control.

For ball bearing wheels, mount one on a mandrel and check lateral runout with a dial indicator. A decent wheel should be under 0.05 mm. Then spin it by hand and feel for roughness. If you detect any kind of crunch at any point in the rotation, that race is damaged. It will fail under load even if it's quiet now.

We rejected a "48 ohm" 28BYJ-48 batch that measured 85 ohms on one coil. The vendor claimed it was "within industry standard." It wasn't. They redid it at their cost. Now every contract we write includes resistance specifications.

Step 5: Test Performance—and Consistency

Don't test one unit out of a batch and call it done. Test at least three units, or 10% of the batch, whichever is larger.

Part-to-part consistency is actually the signal. Good manufacturers hold tight specs. Bad batches scatter, and scatter is what kills you in production when one unit behaves differently from the previous one.

I once tested five "identical" screw-driven actuators from the same order. Stall currents varied by 40%. That variance told us the screws had different leads or the motors had different windings. A single-unit test would have passed. Testing five failed the batch.

Step 6: Check the Things That "Always Work"

Bearings are a commodity product until they aren't.

A ball bearing wheel from a questionable listing can look perfect—polished, clean, good finish—and still have the wrong internal clearance. Put it on a shaft with preload and it gets hot. That's not visible in product photos.

I knew I should verify grease condition on a sealed bearing batch we received, but I thought, "what are the odds?" The odds caught up with me. We had 8,000 units in storage that passed visual inspection and then failed in storage—the grease had separated. Nobody checks grease consistency before installation. Now we do.

Also worth checking:

• Axial play: should meet the spec, not just "feel tight"
• Cage material: counterfeit bearing wheels sometimes use visibly cheaper cages
• Seal type: a "2RS" wheel shouldn't have metal shields instead of rubber seals

Most buyers focus on price, brand, and delivery time. They completely miss verification cost. That's the blind spot.

Step 7: Document Everything

The third time we ordered the wrong quantity, I finally created a verification checklist. Should have done it after the first time.

Keep a record of:

• The supplier and listing number
• Batch codes from the parts
• Your measured values, with test conditions (temperature, voltage)
• Photos of markings and packaging
• The distributor authorization proof you requested

That file serves two purposes. One: it's your evidence if you need a return or a chargeback. Two: it's a history to spot patterns. We used a vendor for years, and they started slipping. Without the log, we would have said "it's basically the same as last time." It wasn't. The batch had mixed ball cages from two different manufacturers.

Oh, and the documentation step is what makes your quality system auditable. If you're ISO-certified, you already know this. If you're not, it's a habit worth building now.

What About "Pete Jackson Gear Drives"?

People still search "what happened to pete jackson gear drives" — a brand that was well known in the performance engine world for timing gear drives. The short answer is that the brand effectively faded from active distribution. The official website stopped being maintained, stock dried up, and support disappeared.

Why bring this up in a linear motion article? Because it's a perfect case of why source verification is part of total cost of ownership. You can still find "new old stock" Pete Jackson gear drives online. Are they genuine? Probably. Can you get a warranty or technical support today? No.

A genuine part from a brand that no longer supports it can be a worse purchase than a current part from a live manufacturer with full documentation. The part number might be identical. The support isn't. When you're evaluating components, ask not just "is this genuine" but "will this brand still be here to support it in five years?" That question saves a lot of pain.

Common Mistakes I Keep Seeing

1. Skipping steps 1 and 2 because the reviews are good. Reviews are easy to fake. Distributor agreements are harder to fake.
2. Testing stepper motors at the wrong voltage. Test at the rated voltage. What I mean is, don't feed a 5V-rated 28BYJ-48 motor 12V just to "see if it moves." You'll burn the coil and then blame the supplier.
3. Only measuring one unit. One unit tells you that one unit is good, not that the batch is good.
4. Trusting visual inspection for bearings. Bearings can look flawless and fail under load. The grease issue mentioned earlier? Never visible from the outside.

Run the seven steps, in order, every time. It takes 20 minutes. The redo when it goes wrong takes weeks.