Ringfeder Torque Chart: What Every Buyer (Not Just Engineers) Should Check

If you're ordering Ringfeder components for the first time, start with the Ringfeder torque chart for the exact product series. Not your old order history, not the part number alone—the chart. This is the single most important thing I learned after ordering power transmission parts for five years.

Quick background: I'm not an engineer. I'm the office administrator at a 180-person manufacturing plant who manages roughly $400,000 a year in MRO (maintenance, repair, and operations) and OEM component orders. I report to both operations and finance. When a machine stops, the maintenance supervisor sends me the request, and I have to get the right part from the right vendor at the right price. I don't calculate shaft stress. I calculate whether the paperwork matches the reality on the machine.

Why the torque chart needs to be part of every Ringfeder order

Here's what happened in 2023, and I still kick myself for it. Our engineer requested a Ringfeder locking assembly for a 40mm shaft. I remembered we ordered the same part a year before, so I skipped the torque check and sent the PO. When the parts arrived, maintenance looked at the drawing, looked at the load spec, and stopped the install. The locking assembly was physically the same size, but the torque rating for that version wasn't high enough for this machine's driven load.

I knew I should pull the current Ringfeder torque chart before ordering. But I thought "what are the odds?" Well, the odds caught up with me. We paid a rush freight fee to get the correct version, and the machine stayed down an extra day. That one mistake probably cost us more in downtime than the part itself.

Why do I say "probably"? Because downtime calculations are never exact. But the invoice for the freight and the extra work order was real enough.

What does the Ringfeder torque chart actually tell you?

The Ringfeder torque chart is the published list of rated torque values for locking assemblies, shaft couplings, and torque management devices. It's not a single chart in one catalog. Each product series—whether it's a locking assembly, a shrink disc, or a coupling—has its own table with values that depend on size, shaft diameter, and mounting configuration.

Three things I always check now:

1. Rated transmittable torque. This is the torque the device is rated to transmit under specified conditions.
2. Tightening torque. The screw torque matters just as much. If you don't tighten the bolts to spec, the chart number is fiction.
3. Shaft and hub size. A locking assembly rated for a 60mm shaft is not automatically the right choice for a 55mm shaft.

The biggest mistake in our plant, before I created a checklist, was ordering from memory. I'd see "RfN 7015" on an old PO and think that was all I needed. It wasn't. The same part code can appear across different sizes with different torque capacities. The chart tells you which one you actually need.

I should note: I'm not going to quote specific torque numbers from memory. Every time I try, I end up mixing up a 45mm version with a 50mm version. That's exactly why I open the chart. At least, that's been my experience with our plant's mix of custom packaging machines.

Don't confuse motor torque with coupling torque

Last year, one of our engineers asked me to buy a NEMA 34 stepper motor, a Gates timing belt kit, and a Ringfeder locking assembly for a prototype machine. That's when I had to learn the difference between all three.

So, what's a stepper motor?

A stepper motor is a brushless electric motor that moves in fixed increments called steps. A driver sends electrical pulses, and each pulse makes the motor rotate by a set angle, usually something like 1.8 degrees per step. Many simple positioning systems don't use a separate encoder because position is proportional to step count, assuming no steps are lost. You'll find them in 3D printers, CNC machines, and pick-and-place equipment.

The "NEMA 34" part is a frame size, not a torque rating. NEMA 34 means the faceplate is about 3.4 inches square. Two NEMA 34 motors can have very different torque depending on motor length, winding, and drive voltage. So if someone hands you a request for a "NEMA 34 stepper motor," you still need to verify the rated holding torque. The NEMA frame size definitions are published in the NEMA ICS 16 standard; they tell you mounting dimensions, not torque output. I had to look that up in 2024 when I kept confusing frame size with power.

Where does the Gates timing belt kit fit in?

The Gates timing belt kit is a synchronous drive system. It uses a toothed belt and matching pulleys to transfer motion without slipping. In that prototype, the NEMA 34 motor drives the belt, the belt drives the shaft, and the Ringfeder locking assembly mounts the pulley to that shaft.

Each of those components has its own torque-related spec. The motor has a holding torque. The belt has a maximum tension and torque capacity. The Ringfeder locking assembly has a rated transmittable torque. If you look only at the motor's torque, you might order a Ringfeder component that is undersized for what the belt system actually delivers.

When Ringfeder might not be the right starting point

This is the part I didn't expect to say as a buyer: there's no one right component for every machine. Ringfeder products work well for lots of torque transmission and shaft-hub connection applications, especially when you need a shrink-fit-like connection without heating or hydraulics. Locking assemblies and rigid couplings can be a smart choice when you need zero backlash and simple installation.

But if your application needs to accommodate significant angular misalignment, or if you need vibration damping between the driver and driven machine, a rigid coupling probably isn't the right first answer. That's not a knock on the product. It's just a mismatch. Asking your applications engineer "which coupling category should we be in" before you look at torque charts will save you a lot of returns.

I recommend Ringfeder when the engineering team has already confirmed that a friction shaft-hub connection is appropriate. If they haven't, start with a conversation, not a PO.

A few things I'd do differently if I started over

If I could go back to 2020, when I first started handling these orders, I'd do three things differently.

First, I'd build a vendor checklist before the first urgent request. We didn't have a formal process for verifying torque ratings against POs. The third time we had to call engineering back to confirm a torque value, I finally created a simple checklist. It should have been there from the beginning.

Second, I'd ask more "dumb" questions. When I first saw "NEMA 34 stepper motor" on a requisition, I didn't ask what it was. I just googled it, then tried to match the torque spec to a coupling. One conversation with the engineer would have saved me an hour. Don't be embarrassed to ask: "Is this the holding torque or the running torque?"

Third, I'd standardize the torque chart as a required attachment for every Ringfeder part number. The chart is not a suggestion. It's the proof that the selected part is right for the load. If a vendor can't tell me where the torque rating comes from, I now treat that as a red flag.

And yes, I still have the regret written into my own PO notes: "Pull the chart. Every time."