Power Transmission Parts: An Admin Buyer's FAQ on Sprockets, Bearings, Stepper Motors, and VFDs

I'm the administrator who turns engineering requests into purchase orders. I've been doing this since 2020 for a 140-person equipment builder in Ohio. That means I touch a lot of Martin Sprocket gear, sealed bearings, motors, and the occasional VFD. I'm writing this in early 2025, so the lead-time observations come from where things stand now. These are the questions I get from the people I buy for—and from suppliers who don't understand why we're picky.

What exactly is Martin Sprocket & Gear?

Martin Sprocket & Gear is a manufacturer of power transmission components. If you need chain sprockets, gears, sheaves, couplings, bearings, or related parts, they either make it or stock it. Their main advantage for us is the distribution network: multiple manufacturing locations and warehouses across the U.S. means a part can usually get to us in two or three days without going through customs or overseas shipping.

If you're trying to find them online, the site is martin-sprocket.com. And when I say the name to our internal people, it's usually described as simply martin sprocket. Same company, same catalog.

How do I read a part number like martin sprocket gear 40bs12 1?

You look it up. I don't mean that as a brush-off. Part numbers are a code, not a language. That string has a specific meaning for a specific sprocket configuration. For example, 40bs12 1 translates roughly to a 40B series sprocket with 12 teeth and a 1-inch bore. But I still verify it against the catalog because a wrong sprocket means a downtime call from production.

I keep the Martin catalog open in a tab—the online catalog, I mean. The paper version is a brick. If maintenance says, I need the sprocket for the #40 conveyor, I don't guess. I ask for the number or the old part. When they give me the full Martin number, my job is to make sure it's real, available, and priced.

What about a part number like martin sprocket gear srl090 095?

That one I want to say is a roller chain sprocket identifier, but I'm not going to pretend I know it by heart. The SRL part of the number is shorthand that points to a family in the catalog. The 090 and 095 are probably dimension or bore references. When I saw this number for the first time, I called our distributor, gave them the full string, and they confirmed the bore and width before quoting.

Here's the thing: if you're a buyer, you don't need to memorize every series. You need to know where to find the definition. Martin's catalog does that. If you're on the phone, a customer service rep can translate it. But the important part is to get the whole number, because a missing letter or digit can change the part completely.

What's a VFD?

A VFD is a variable frequency drive. It's an electronic controller that adjusts the speed of an AC motor by varying the frequency and voltage going to it. In practice, that means a fan doesn't have to run at full speed all day, a pump can run at 80 percent, and a conveyor can slow down for cleaning or alignment.

Do you need one? It depends. If a motor is running at fixed speed and you never change it, a VFD is probably wasted money. If you're constantly slowing down or stopping, then a VFD can also give you controlled deceleration—which is nice for stopping a heavy line gently instead of slamming it.

One thing we learned: not every motor is inverter-rated. A standard motor can overheat on a VFD at low rpm if it's not designed for it. Check the motor nameplate or talk to someone before you throw a VFD on a fifty-year-old motor.

When is a closed loop stepper motor worth the extra cost?

I'm not a motion-control engineer, but I've ordered enough of them to see the pattern. A closed loop stepper motor is a stepper motor with an encoder on the back. The drive knows where the shaft actually is. If a step gets missed, the system can correct it or alarm out instead of continuing in the wrong position.

Is it worth the premium? It depends on how bad a missed step is. I bought a closed loop stepper motor for a labeling machine because open-loop steppers kept losing position, and the mislabeled labels were costing us a shift of rework. We also replaced a NEMA 23 stepper with a NEMA 23 closed loop version, so it fit in the same footprint. That was an easy decision. If the motion is simple and a jig prevents misses, a standard stepper might be fine.

What is a roller ball bearing?

When someone sends me a requisition that says roller ball bearing, I send back a question: do you mean a ball bearing or a roller bearing? Because those are two different things. A ball bearing uses balls and handles moderate loads with low friction. A roller bearing uses cylindrical or tapered rolls and handles heavier radial loads.

I've seen the phrase used as a catch-all for any round bearing in a housing, but it's not a formal category. If you're looking at a conveyor roller, you may actually need a mounted ball bearing with a sealed insert. If a shaft is at an angle or there's heavy side load, then you'd look at a spherical roller bearing or a tapered roller bearing.

For our plant, most of the items codified as roller ball bearing turn out to be standard insert ball bearings. But the label itself isn't enough to order from. You need the shaft diameter, the width, the housing style, and the fastener type.

When does expedited shipping actually make sense?

This is where I admit I've changed my mind. Early in this role, I considered expedite fees as waste. Now I see them as buying certainty. In March 2024, we paid an extra $180 for rush delivery on a Martin sprocket gear. The alternative was missing a customer acceptance test worth $15,000. I had two hours to decide before the rush cutoff. Normally I'd have gotten three quotes, but there was no time. I kept asking myself whether $180 was worth potentially losing that test. It obviously was.

Look, I do not believe every rush order is justified. If we messed up our inventory planning, that's our problem, and sometimes a two-day wait is fine. But when a deadline is real, I stop trying to save $100 and start asking about the ship date, the carrier, and the tracking number. I've been told next-day and then watched the label sit at the warehouse for a day. That's not expediting, that's a promise without a contract.

This worked for us because we're a mid-size shop with predictable demand. If you're a plant running 24/7, your version of expedite is probably a stocked spare, and that changes the math entirely.

How many suppliers should I keep for power transmission parts?

We use two main suppliers plus a local motor shop. One is a broad-line industrial distributor. The other is our direct account for Martin Sprocket gear and sprockets. The motor shop handles repaired motors and VFD installations.

Why not eight suppliers? Because I've been down that road. More vendors means more quotes, more invoices, more issues with shipping terms. In 2024, we consolidated and cut our ordering time from about six hours a month to two. The tradeoff is less price-shopping, but for standard parts, the relationship usually gives us better service than the penny we'd save elsewhere.

That said, I should add that we keep a backup on critical items. If our main distributor can't get a special steel sprocket quickly, we have a second source who can. I don't call it a relationship, but their number is in my phone.