A load cell reports force electrically. Somewhere inside, a shaped piece of metal gives way by a fraction no eye would catch; gauges riding on it convert that yielding into a change of resistance, the bridge behind them into a voltage, and a certificate written against known weights into pounds.
What decides a load cell's capabilities, more than almost anything else, is how force gets into it. The sensing physics is common to the whole category; the interface is what varies, and the interface determines what the sensor can and cannot do.
A pressed interface — a button, a flat face, a convex dome — can only be pushed. There is nothing holding the two parts together, so the moment you try to pull, they simply separate. Compression-only isn't a marketing decision on those designs; it's arithmetic.
A bore lets an existing component pass through, so the sensor joins a load path already in place without interrupting it. Useful for retrofitting measurement onto a bolt or shaft, and constrained by what will fit through the hole.
A threaded interface changes the picture entirely, because threads carry tension. Screw a fitting into a stud and the connection resists being pulled apart as readily as being pushed together. That single mechanical fact is what allows one sensing element to serve both directions — and it's why a surface stud mount design, which otherwise resembles a bolted-down compression sensor, can measure a pull as competently as a push.
Threads bring their own considerations, though, and they're less obvious than they look. A threaded joint is not a single defined interface but a range of possible ones, depending on how far the fitting is screwed in, what it bears against, and whether it stays put. That variability has consequences for measurement which are worth understanding before installation rather than after.
Sensors built this way — heat-treated 17-4 PH stainless, bolted to a flat surface, load applied through a central stud — suit materials and structural testing, aerospace and automotive component work, industrial automation, and any test fixture where the load has to be positively attached rather than merely rested against.
Standard electrically. The threaded load path is where this design deserves specific attention.
Signal. Excitation at 10 VDC brings the bridge to life. Strain the element and the gauges answer by shifting resistance; balance gives way and a few thousandths of a volt appear. Because that figure is a proportion of what you fed in, sensitivity has to be quoted per volt. The rest is conditioning and arithmetic against the certificate on file — a certificate written for one excitation voltage and no other.
Thread engagement is a measurement variable. This surprises people, and it shouldn't. Where a fitting sits in a threaded connection changes how load transfers into the sensing element, and the effect is measurable rather than theoretical. Published testing by a force calibration laboratory found two adapters differing only in engagement depth — 1.5 inches versus 0.5 inches — produced readings of 10,001.5 lbf and 9,942.3 lbf on the same applied load. That is a 0.59% difference on an instrument capable of far better, caused by nothing but how far a fitting was screwed in. The same work found meaningful differences between loading through threads and loading against a base.
What follows from that. Three things. Engagement should be adequate — the usual guidance is engagement at least equal to the thread diameter, with the first several threads carrying most of the strength and additional depth giving diminishing returns. Engagement should be consistent, because a reading depends on it. And ideally the sensor should be calibrated with the same adapter arrangement it will use in service, since a calibration performed with one configuration does not perfectly describe another. Locking an adapter permanently in place removes the variable altogether, which is why calibration laboratories favour integral adapters.
Alignment still matters. Whatever the stud is pulled by needs to pull straight. Tug at an angle and part of the effort becomes a bending moment, arriving at the gauges thoroughly mixed in with the tension you wanted and impossible to pick apart afterward. Where the structure cannot guarantee a straight pull, self-aligning hardware — rod ends, swivels, clevises — lets the load find the axis rather than forcing the sensor to accept whatever direction the fixture imposes.
And the base is part of the system. A surface-mounted cell transmits load into whatever it is bolted to. That surface needs to be flat, clean, and stiff enough not to deform under your peak load, with the mounting fasteners evenly tightened. A base that flexes puts a moment into the sensing element before any test load arrives.
Choosing between mounting styles is usually a question about your fixture rather than about measurement performance. Our application engineers can work through it with you quickly.
Start with direction. Does your application only ever push, or does it also pull? This single question eliminates most of the catalogue. If the load is purely compressive and simply rests on the sensor, a pressed-interface design is simpler and often cheaper. The moment tension enters the picture — even occasionally, even just to lift a fixture back off — you need a positive attachment, and that means threads.
Then consider how the load is delivered. A stud gives you something to screw into, which suits test frames, actuator rods, threaded couplings and any arrangement where the load path is assembled rather than stacked. Ask what will attach to it, whether that attachment can be kept aligned with the axis, and whether it will be removed and refitted regularly — because if so, engagement consistency becomes something to manage deliberately.
Plan the adapters as part of the purchase. Rod ends, couplings and threaded adapters are not accessories on a stud-mount sensor; they define the load path. Decide what they are, keep them consistent, and consider having the sensor calibrated with them fitted if the measurement needs to be defensible.
Size capacity honestly in both directions. Hand-assembled fixtures have a habit of seeing loads the test never called for — a wrench and a long arm can outdo a test programme without anybody meaning to. Set your plausible maximum beside the safe overload figure, and fit a mechanical limit if the geometry allows one.
Prepare the mounting surface. Flat, clean, hard enough not to indent, and stiff enough not to dish at peak load, with adequate thread engagement in the base for the mounting fasteners. On surface-mounted designs the structure beneath is as much part of the instrument as the sensor itself.
Then environment, calibration direction and readout. The compensated band and the drift coefficients between them let you predict thermal error instead of meeting it unprepared. Settle which direction needs certifying, because compression and tension are separate exercises with separate certificates. On the electronics, an amplifier signal conditioner module suits a sensor feeding acquisition equipment, while a digital display brings alarms, analog output and logging in one box. Units that travel between fixtures are the case for Cal-Teds plug and play, which spares somebody typing calibration figures under pressure.
Describe the fixture, the direction of loading, what attaches to the stud and what the sensor bolts to, and we'll help you specify it properly. Standard capacities are stocked for quick despatch, and educational pricing is available to schools and universities.
SSM Series Load Cell Applications.
The Transducer Techniques SSM Series surface stud mount load cells, designed for both tension and compression applications, are specialized devices used for precise force measurements.
- Material Testing: SSM Series load cells are commonly used in material testing applications, including tensile and compressive tests on various materials such as metals, plastics, ceramics, and composites.
- Structural Testing: In structural engineering and construction, SSM Series load cells are employed to measure the forces applied to building components, bridges, and other structures.
- Aerospace Testing: The aerospace industry relies on SSM Series load cells for structural testing of aircraft components, including wings, landing gear, and fuselage components.
- Automotive Testing: Automotive manufacturers and testing facilities use SSM Series load cells for quality control and testing of vehicle components, such as suspension systems, chassis, and steering mechanisms.
- Industrial Automation: In industrial automation systems, SSM Series load cells are integrated into machinery and equipment for monitoring and controlling forces in various manufacturing processes.
- Product Development: Engineers and researchers use SSM Series load cells during product development and prototyping to evaluate the performance, durability, and structural integrity of new designs and components.
- Quality Control: Quality control processes in various industries benefit from SSM Series load cells to verify that products meet specific force and load specifications.
- Research and Testing: These load cells are used in research laboratories and testing facilities for a wide range of experiments and tests that require precise force measurement.
- Educational Laboratories: Educational institutions incorporate SSM Series load cells into engineering and materials science laboratories to teach students about force measurement principles.
- Custom Machinery and Equipment: Manufacturers and research facilities integrate SSM Series load cells into custom-built machinery and equipment designed for specialized testing and manufacturing processes.
Their versatility and reliability contribute to improved product quality, safety, and process efficiency.
Frequently Asked Questions
What does "surface stud mount" actually mean?
It describes both halves of the installation. The sensor is surface mounted — bolted down flat onto your structure through threaded holes in its base — and the load is applied through a threaded stud at its centre rather than pressed onto a face. So the sensor is fixed to your fixture at one end and positively attached to your load path at the other, which is what distinguishes it from a design that simply sits between two surfaces.
Can the SSM really measure tension as well as compression?
Yes, and the stud is precisely why. A load cell with a pressed face can only ever be pushed — there's nothing holding it to the thing applying force, so a pull just separates them. Threads hold in both directions, so a fitting screwed onto the stud resists being pulled apart as readily as being pushed together. That mechanical fact is what lets one sensing element serve both directions, and it's the main reason to choose this configuration over a compression-only design.
What capacities does the SSM Series cover?
Nine: 100, 200, 500, 1,000, 2,000, 2,500, 5,000, 8,000, and 10,000 lb, all at the same price. Because accuracy specifications are percentages of rated output, that single price across the range means nothing pushes you toward over-specifying capacity — choose the model that matches the force you actually work at and keep your absolute accuracy where it belongs.
How accurate is the SSM Series?
Nonlinearity and hysteresis are each 0.15% of rated output, nonrepeatability is 0.05%, and zero balance is 1.0%. The nonrepeatability figure is the one worth dwelling on for most test work, since it describes how consistently the same applied load returns the same reading — and unlike the other two, it cannot be calibrated out. At 0.05% it supports genuine comparison between one test and the next.
What holds the SSM down to my structure?
Eight threaded holes in the base, taking fasteners up from beneath into the sensor body. Eight points distribute the clamping load evenly around the base rather than concentrating it, which matters because uneven clamping is itself a source of offset. The mounting surface needs to be flat and at least 2 inches in diameter so the sensor is fully supported, and stiff enough not to deform at your peak load.
Is tension calibration included, or is it an option?
Compression calibration is standard; tension calibration is the TC-CAL option. This is worth catching on a bidirectional product, because the stud makes tension mechanically possible whether or not it's been certified. If your application pulls — or pulls sometimes — specify tension calibration at order time. Compression and tension travel different load paths through the sensor, so a compression certificate describes compression and nothing beyond it.
How much does the SSM deflect under load?
0.002 inches at rated output. That's small enough that inserting an SSM into a test frame or fixture doesn't meaningfully change the assembly's stiffness, which matters when the sensor is part of a load path you're characterising. Low deflection also means the sensor settles quickly rather than continuing to move as force is applied.
What is the SSM made from, and how does temperature affect it?
Heat-treated 17-4 PH stainless steel with sealed bonded foil strain gauges. Compensation runs 60° to 160°F, with a safe range of −65° to 200°F; within the compensated band, output drifts 0.005% of load per °F and zero drifts 0.005% of rated output per °F. Both coefficients being published means a known temperature change becomes a number you can calculate rather than an effect you absorb.
Where does the SSM sit against your other 10,000 lb sensors?
Its distinguishing feature is the combination of a bolted-down base and a threaded load stud, giving positive attachment at both ends. Our load button designs at similar capacities are compression only, since a pressed face cannot transmit a pull. Our through-hole designs suit situations where an existing bolt or rod passes through the sensor. If you need to screw your load path into the sensor and pull as well as push, the SSM is the configuration built for it.
Can I get the SSM with the plug-and-play TEDS option?
Yes, OPT-TEDS holds the unit's calibration data at the connector so a compatible instrument applies it automatically instead of relying on manual entry. That's particularly worth having on a bidirectional sensor, since a unit carrying both compression and tension calibration data has more to get wrong if someone is transcribing figures by hand.
Questions From The Field
Does it matter how far I screw my fitting onto the stud?
More than almost anyone expects, and this is the single most useful thing to know about a stud-mount sensor. Published testing by a force calibration laboratory compared two adapters differing only in thread engagement — 1.5 inches against 0.5 inches — and recorded 10,001.5 lbf versus 9,942.3 lbf for the same applied load. That's a 0.59% difference produced by nothing but engagement depth, on an instrument capable of far better. Engagement changes how load transfers into the sensing element, so it is a measurement variable, not an assembly detail.
How deep should the fitting engage, then?
The general guidance is engagement at least equal to the thread diameter. The first several threads carry most of the strength, with additional depth giving diminishing returns structurally — but the point isn't only strength, it's consistency. Pick an engagement, make sure it's adequate, and then reproduce it every time. An adapter locked permanently in place removes the variable entirely, which is why calibration laboratories prefer integral adapters where the application allows.
Should I have the SSM calibrated with my adapter fitted?
If the measurement has to be defensible, yes. Because engagement depth and the adapter arrangement both affect how load enters the sensor, a calibration performed with one configuration doesn't perfectly describe another. Calibrating the assembly you'll actually use eliminates that gap. If you send us the sensor with its adapters, we can calibrate it as a unit — and if you change adapters later, treat that as a reason to re-verify rather than assuming the certificate still applies.
My readings changed after I swapped the fitting on the stud.
That's consistent with what the thread engagement research shows rather than a sign of a fault. A different adapter means a different engagement depth, possibly a different bearing arrangement, and therefore a slightly different load path into the sensing element. Re-zero after any change, verify against a known load if you have one available, and if the shift is larger than you can live with, standardise on one adapter and keep it fitted.
Do I need a rod end or swivel on the stud?
If you can't guarantee the load pulls straight along the stud's axis, yes. The sensor measures force along that axis, and anything arriving at an angle adds a bending moment it cannot distinguish from real load. Self-aligning hardware lets the load find the axis instead of forcing the sensor to accept whatever direction your fixture provides. Note the trade-off, though: a rod end is another threaded joint, so whatever you fit, keep its engagement consistent for the reasons above.
Should I use a jam nut on the stud fitting?
It's worth considering wherever the joint sees repeated loading or vibration, since a fitting that gradually backs off changes engagement depth and therefore your readings — which would appear as a slow, unexplained drift rather than an obvious failure. What matters most is that engagement stays where you set it. Whether that's achieved with a jam nut, a thread-locking compound suited to your temperature range, or a permanently installed adapter depends on whether you need to remove the fitting again.
My mounting surface is smaller than the sensor base. Is that acceptable?
No — the base needs full support on a flat surface of at least 2 inches diameter. A partially supported sensor bears on only part of its base, which puts a bending moment into the sensing element before any test load is applied and makes the reading depend on how it happened to sit. If your fixture can't provide that, a hardened flat mounting plate between fixture and sensor is usually a straightforward fix and far cheaper than absorbing an unknown error.
My tension readings and compression readings don't seem consistent with each other.
Check first whether you actually hold a tension calibration, since compression is what ships as standard — applying a compression certificate to tension data is the most common explanation. Beyond that, the two directions genuinely load the sensor differently: in tension the stud threads carry the load, while in compression some of it transfers through the bearing arrangement. That's why they're certified separately. If you have both calibrations and the discrepancy persists, look at whether the adapter or fixture behaves differently in the two directions.