The Lovejoy Coupling Ordering Checklist: 6 Steps I Wish I Had in 2018

I'm a senior buyer handling transmission component orders for seven years. I've personally made (and documented) nine significant ordering mistakes, totaling roughly $8,000 in wasted budget. That's why I maintain our team's ordering checklist—and that's what I'm sharing here.

If you're ordering a Lovejoy coupling—or anything connected to a motor shaft, honestly—this checklist is for you. It takes ten minutes and covers the six checks I wish someone had forced me to run back in 2018.

A note before we start: I'm focused on Lovejoy couplings here, but most of these steps apply to any transmission component order. The mistakes are the same. So is the math.

Step 1: Identify the coupling family before you open the catalog

Lovejoy makes several coupling families: Jaw (L/AL/CN series), Gear (G series), S-Flex, and Hydraulic (H series). They look different, mount differently, and have completely different ratings. A Lovejoy coupling L-100 (jaw type) is not a substitute for a Lovejoy hydraulic coupling, and no amount of "it should fit" changes that.

If you're replacing an existing coupling, measure what's on the machine. Don't guess from the shaft size alone. In my first year (2018), I ordered the right series but the wrong bore for a 40-piece order. Every single item had the same issue and needed re-machining. $890 in redo costs, plus a one-week delay. That's when I learned to verify the part number, then verify it again.

The L-100, specifically, is a jaw coupling with a bore range roughly from 1/4" up to 1-1/8", depending on hub configuration. Lovejoy publishes full dimensional data in their engineering catalog. Check the catalog. Don't trust my paragraph, and don't trust the part number stamped on a worn hub. Measure.

Step 2: Confirm bore, keyway, and set screw specs exactly

The catalog bore range tells you what's possible. It doesn't tell you what you need. Three things to verify:

• Bore diameter. The actual measured shaft diameter, not the nominal motor size on the nameplate. I've caught shafts that were 0.02mm off from the nameplate spec. Usually fine. Not always.
• Keyway width and depth. Metric and imperial keys are not the same. H7 tolerance (per ISO 286) is common for metric bores, but confirm that's what your shaft spec requires.
• Set screw thread and position. One set screw or two? What thread? It matters when the coupling sits in a tight space and you can't get a driver in.

I once told a vendor "standard size." I meant "the size we always order." They heard "off-the-shelf inventory." We discovered the mismatch when the couplings arrived and spun freely on the shaft. $1,200 of coupling inventory, freight, and expedite fees, gone. We were using the same words but meaning different things. That failure was mine more than theirs. Now I send the critical dimensions in writing with every order—bore, keyway, screw size—even for parts we buy monthly. It's a two-minute email that has saved us thousands.

Step 3: Don't forget the spider insert

Jaw couplings use a spider (the elastomer insert) between the hubs. Durometer determines how much misalignment and vibration the coupling absorbs. 80A is the general-purpose choice; 92A is stiffer, for higher shock loads. Don't hold me to this—the Lovejoy catalog has a full selection guide—but that's the general split.

Here's the embarrassing one. I once ordered 15 L-100 couplings without the spiders. The hubs arrived on schedule. The installation crew was ready. No inserts. Production stopped for half a day while we expedited a $12 part. A $4,000 production interruption caused by a $12 omission. That's total cost thinking in its simplest form: the unit price is meaningless if the order isn't complete. We now add the spider to every order as a line item with a red check mark. Sounds dumb. Works. That simple addition killed an entire category of mistakes for us.

Step 4: Match the motor and controller to the load

A coupling can't compensate for an undersized motor or a mismatched controller. If you're using stepper motor controllers, verify the controller's current rating and supply voltage against the motor's specs. A mismatch doesn't fail immediately. It runs fine under no load, then stalls the moment the load comes up. I've watched teams diagnose that as a "bad coupling." It wasn't.

For smaller builds, the MG90S servo motor is everywhere. It's a micro servo with metal gears, roughly 1.8 kg/cm stall torque at 4.8V and 2.2 kg/cm at 6V. The output shaft uses a ~4.8mm spline. If you're ordering a hub or coupling for an MG90S servo motor, the bore has to match that actual spline dimension—not the nearest standard-size bushing in your stock. I still kick myself for ordering a batch with a 6mm bore because "6mm is standard." It wasn't standard for this part. It was a leftover spec from a different motor. $300 in unusable hubs. And the kicker? They were standard. Standard for something else. "Standard" means nothing without a drawing.

Step 5: Check linear motion components before guessing sizes

Not strictly coupling-related, but the same mistake pattern shows up here. People ask "what size is an LM8LUU linear bearing?" and answer from memory. The correct answer: 8mm inner diameter, 15mm outer diameter, 45mm length. The "L" means long—a regular LM8UU is 24mm. The 8mm bore and 15mm OD are the numbers that matter for shaft matching.

I've seen two orders fail because the bearing was spec'd from memory without measuring the shaft. Metric shaft. Imperial housing. And the bearing between them was exactly the wrong thing. Not great, not terrible. Just wrong. $175 in return shipping plus four days of delay. The bearing follows the shaft. Measure first, spec second. And if you're replacing an LM8LUU, check the housing pocket too—the 45mm length won't fit in a standard LM8UU housing. Ask me how I know.

Step 6: Run the total cost check before you hit approve

The cheapest quote gets attention. It shouldn't get automatic approval. Total cost of ownership includes the quote, shipping, lead time, and the likelihood of rework. Any one of those can turn the "low price" vendor into the most expensive one.

Real example from my notes: an $85 L-100 coupling with a three-week lead time is not cheaper than a $120 one that arrives tomorrow—not if the line is down while you wait. And a low unit price means nothing if you're spending hours chasing order status updates. I calculate total cost before comparing vendor quotes now. It changed how I buy.

Since we started using this checklist, we've caught 47 potential errors in 18 months. Three of those would have shut down a production line. I'm not going to pretend that's skill—running checklists isn't glamorous. But it's cheaper than the alternative. So glad we ran it. Almost skipped the check on a rush order once. That was the one with a $6,000 potential error hiding in the bore size. The numbers on the shaft and the numbers on the P.O. didn't match. Caught it before the order went out. That's the quiet win nobody sees.

Common mistakes I still see (and have made myself)

Three reminders, even after running the six steps:

1. Re-check repeat orders. "It's the same as last time" is the most expensive phrase in procurement. It wasn't the same. The motor spec changed. The shaft changed. Repeat orders get the same review as new ones.

I skipped the final review once because we were rushing. "Basically the same as last time." It wasn't. $400 mistake. Period.

2. Get it in writing. A phone confirmation is not documentation. Get an email or a drawing sign-off from the vendor. If the wrong coupling shows up, your written confirmation is what gets the replacement covered without a fight.

3. Measure, then measure again. Bore, shaft, keyway, thread. Measuring is free. Reordering is not.

Is ten extra minutes of checking worth it? Sometimes. Depends on context. But in my experience, ten minutes at the desk beats the phone call telling a customer the wrong coupling is sitting on the dock.