A load cell is a piece of metal instrumented to report how hard it is being worked. Buried gauges shift in resistance as the metal strains, a bridge circuit reads the imbalance in millivolts, and a certificate maps those millivolts onto pounds.
Nearly every load cell is something you add. You interrupt a load path, insert an instrument, and accept the consequences: extra length, extra joints, extra fittings, and a component that was not in the original design. On existing equipment that is often the hardest part of the job, and sometimes it is the reason the measurement never happens.
A load pin works the other way round. Almost every machine that lifts, pulls or pivots already has pins in it — shackle pins, clevis pins, pulley shafts, sheave pins, linkage pins — each one already carrying the full load. Replace one of them with a pin that also reports, and you have instrumented the machine without changing it. Nothing gets longer, nothing gets softer, no new joint appears, and the load path is exactly the load path the designer intended.
That substitution changes what is being measured and how.
A pin measures shear, not tension or compression. Picture a pin through a clevis: the two outer ears push one way, the eye or link in the middle pulls the other. Between them, at the boundaries of the loaded centre section, the pin is being sheared — two planes trying to slide past one another. Gauges buried in the pin read that shear. It is a different quantity from the axial strain almost every other load cell responds to, and it is why a pin can be an accurate instrument while looking exactly like a pin.
Where the force lands along the pin is baked into the certificate. Because the shear planes sit at fixed positions along the pin, the calibration assumes force arrives at those positions. Change where the ears bear — a clevis of different width, a spacer left out, a link narrower than intended — and the shear planes no longer line up with the sensing. The dimensions published for each model are not just for checking it fits; they describe the loading arrangement the certificate was written for.
And a pin only measures in one direction around its own axis. The gauge circuit is oriented in line with the expected load vector. Rotate the pin in its bore and the measuring plane rotates away from the force, so the reading falls off — steadily, quietly, and without anything appearing to be wrong. This is the failure mode unique to load pins, and it is why anti-rotation hardware is not optional.
Sensors of this kind belong in marine and offshore work on rigging, mooring lines and lifting equipment, in cranes, hoists and lifting attachments, on pulley and sheave shafts, in excavator and heavy machinery linkages, on offshore drilling equipment, and anywhere a load has to be known on machinery that already exists.
The electrical half is conventional. The mechanical half is where a load pin differs from everything else, and it is worth going through properly because the installation decides the result more than the sensor does.
Signal. A 350 ohm bridge, 10 VDC across it, and 2 mV/V back at rated load — twenty millivolts or so, quoted per volt because what comes out is a fraction of what went in rather than a number of its own. From there it is conditioning and arithmetic against the calibration data, which was recorded at one particular excitation voltage.
Orientation is the specification nobody expects. Manufacturer installation guidance for this product class is explicit that the strain gauge circuit is positioned in line with the load vector, and that anti-rotation hardware is required to maintain the angular relationship between the pin and the force. The method depends on which side of the joint is fixed: a key pin where the clevis is held and the load angle varies through the eye, keeper plates where the eye is fixed and the angle varies through the clevis, or an anti-rotation bracket where the structure cannot be modified. Below two inches in diameter a keeper plate typically restrains rotation in one direction only, so a retaining ring or nut is also needed — which is what the snap ring groove on the smaller models is for.
Fit matters, but not in the way people assume. Published guidance gives diametral clearances by pin size — on the order of a thousandth of an inch for a precision fit under an inch of diameter, a few thousandths for an average fit, and rather more for a loose one. The useful part is the conclusion that goes with it: larger clearances are not in themselves a serious accuracy problem, but they concentrate the bearing contact into a smaller area, and it is that raised contact stress which starts to cost accuracy at high loads. Fit is a bearing question first and a measurement question second.
Your clevis is part of the instrument, and it can be the thing that fails. The bearing surfaces of the clevis and the eye have to be strong enough not to deform under load. Installation guidance for load pins notes plainly that at high loads the yield stress in the clevis metal can produce measurement errors that have nothing to do with the pin. A pin fitted into soft or undersized ears will read badly, and the pin will get the blame.
Nothing should push the pin along its own axis. Guidance for this class is direct about it: no axial forces should be applied to the pin during installation or in use. A pin that is being forced sideways through its bore, or driven in against resistance, is being loaded in a direction the design does not account for.
Materials and connection. The pin is heat-treated 17-4 PH stainless steel with a stainless steel moulded connector system, which is the combination that makes marine and offshore service realistic — salt-laden air attacks unprotected sensors steadily, and on this product the electrical exit is built as part of the sealed structure rather than as a cable emerging from a gland.
Specifying a load pin is mostly a dimensional exercise, and it is one worth doing with us rather than from a table — because a pin that is nearly the right shape is not a pin that nearly works.
Start with the joint you already have. Measure the bore diameter, the thickness of each outer ear, the width of the centre link and the total width across the joint. Those figures decide which model can be used, because they have to correspond to the loading dimensions the pin is calibrated around. Send them to us with a sketch and we will tell you honestly whether a standard pin fits or whether the job wants a special.
Work out how rotation will be prevented before you order. This is the step most often left until the pin arrives, and it is the one that decides whether the readings mean anything. Establish which side of the joint is structurally fixed and which one moves, since that determines whether a key, a keeper plate or a bracket is the right approach, and whether the surrounding structure needs modifying at all. Ask us at the enquiry stage, not on installation day.
Rate the pin for the worst moment, not the working day. Rigging, mooring and lifting loads are rarely steady. Snatch loads, swinging, wave action and sudden stops all produce peaks well above the working figure, and the pin experiences everything the joint experiences. Size against the credible worst case rather than the nominal working load, keeping that peak inside the safe overload rating.
Be realistic about accuracy, and about what it is for. A load pin is a structural component first and an instrument second, and the published figures reflect that. It will not match a laboratory load cell, and it is not trying to. What it offers instead is a measurement that exists at all on equipment where inserting a conventional sensor would mean redesigning the machine. For monitoring, protection and load awareness that is exactly the right trade; for certifying a number to four significant figures it is not.
Order the mating assembly with the pin. There is a connector on every pin, so you cannot use one without a mating assembly — and it comes in a choice of cable lengths. Choose the length deliberately and order one per pin — a load pin without its cable assembly is an expensive clevis pin.
Then decide what reads it. Feed it to an amplifier signal conditioner module if a control system is doing the thinking, or to a digital display if someone needs to see the number and be warned when it climbs — on rigging and lifting work that warning is frequently the whole reason the pin is there. Where pins get swapped around a fleet, Cal-Teds plug and play keeps each one's calibration data with the pin itself.
Give us the joint dimensions, the loads including the peaks, how the assembly moves and what the reading is for, and we will work out the right pin and the hardware to hold it. Standard sizes are stocked and specials are routine on this product.
CLP Series Load Cell Applications.
The Transducer Techniques CLP Series clevis load pins are specialized instruments designed for accurate and highly reliable force measurement applications in both marine and industrial settings, constructed from heat-treated 17-4 PH stainless steel with a stainless steel molded connector system for harsh industrial environments.
- Marine and Offshore: The marine and offshore industries use CLP Series load pins for measuring and monitoring loads on various components and structures, including rigging, mooring lines, and lifting equipment.
- Shackle Pin Replacement: These load pins serve as direct replacements for shackle pins, offering accurate load measurement capabilities while maintaining the functionality of shackles.
- Clevis Pin Replacement: In industrial and construction settings, CLP Series load pins function as reliable replacements for traditional clevis pins, providing the added capability of load measurement.
- Pulley Systems: Pulley system applications employ these load pins to monitor the loads applied to pulley shafts, ensuring safe and efficient operation.
- Testing Laboratories: Testing laboratories use these devices for conducting tension and compression tests on a wide range of materials.
- Lifting and Rigging Equipment: Integration into lifting and rigging equipment provides real-time load monitoring, ensuring that loads remain within safe operating limits.
- Industrial Automation: Industrial automation systems employ these load pins to measure and control forces in manufacturing and assembly processes.
- Construction and Heavy Machinery: The construction and heavy machinery industries use CLP Series load pins for load measurement in applications such as crane hooks, lifting attachments, and excavator buckets.
- Offshore Drilling: Offshore drilling operations employ these load pins to measure loads on drilling equipment and components.
- Research and Development: Research and development teams use these load pins during product development and testing to evaluate the performance and load-carrying capacity of components and structures.
The Transducer Techniques CLP Series clevis load pins are known for their accuracy, reliability, and high load capacity, making them valuable tools for force measurement in marine, industrial, and construction applications.
Frequently Asked Questions
What is a clevis load pin and how does it measure force?
It is a pin that replaces one your machine already has — a shackle pin, clevis pin or pulley shaft — and reports the load it is carrying. Rather than measuring stretch or compression along an axis, it measures shear: the outer ears of a clevis push one way while the link in the middle pulls the other, and between them the pin is being sheared across two planes. Strain gauges inside read that shear. Because the pin was going to be in the joint anyway, nothing about the assembly has to change to instrument it.
What capacities does the CLP Series cover and what do they cost?
From 750 lb to 200,000 lb. The CLP-750 and CLP-1.5K are $1,145; the CLP-3K, 6K, 12.5K and 18K are $1,210; the CLP-30K and CLP-50K are $1,245; the CLP-75K is $1,435; the CLP-100K is $1,560; the CLP-125K is $2,225; and the CLP-200K is $3,400. Because a pin is defined by its dimensions as much as its rating, the capacity you need and the pin that fits your joint are two separate questions — send us both.
Why does a load pin have to be prevented from rotating?
Because the gauge circuit inside is oriented in line with the direction the load is expected to come from. Turn the pin in its bore and the sensing plane turns away from the force, and the reading drops off in proportion — smoothly, with nothing to indicate a problem. Installation guidance for this product class treats anti-rotation hardware as a requirement rather than an accessory, and the right method depends on your joint: a key where the clevis is fixed, a keeper plate where the eye is fixed, or a bracket where nothing can be modified. Settle it before the pin arrives.
How accurate is the CLP Series, and why is it not tighter?
Nonlinearity and hysteresis are each 0.50% of rated output, with nonrepeatability at 0.15% and zero balance at 1.0%. Those figures are looser than our laboratory load cells, and the reason is inherent to the format rather than a shortcoming: the pin has to be a structural component first, it is loaded through bearing surfaces whose contact distribution is not fully controlled, and it works inside your clevis rather than inside a fixture we designed. What you get in exchange is a measurement on equipment that could not otherwise be instrumented at all. For load monitoring, overload protection and knowing what a machine is doing, that trade is usually the right one.
Do I have to change my shackle or clevis to use one?
Usually not, which is the point of the product — but the dimensions have to correspond. The pin's calibration assumes load arriving at particular positions along its length, so the bore diameter, the thickness of each outer ear and the width of the centre link all need to match the model. Measure the joint first and send us the figures with a sketch. Where a standard pin does not correspond, a special made to your dimensions is routine on this product rather than exotic.
What clearance should there be between the pin and the bore?
Published guidance for load pins works in three bands — roughly a thousandth of an inch for a precision fit below an inch of diameter, two to four thousandths for an average fit, and more for a loose one, with the figures scaling per inch of diameter on larger pins. The useful part is what that guidance concludes: a larger clearance is not in itself much of an accuracy problem, but it concentrates the bearing contact into a smaller area, and the resulting contact stress is what costs accuracy at high loads. Treat fit as a bearing question first.
What is the CLP made from, and will it survive marine service?
Heat-treated 17-4 PH stainless steel with a stainless steel moulded connector system designed for harsh industrial environments. That combination is why marine and offshore work is a listed application — salt-laden air is conductive and attacks unprotected sensors steadily rather than dramatically, and on this design the electrical exit is part of the sealed structure rather than a cable emerging through a gland. For permanently submerged service or anything unusually aggressive, describe the installation to us before ordering.
What do I need to order alongside the pin?
A mating assembly, one per pin, which is required rather than optional — every CLP uses a connector, so without it there is nothing to wire to. Four cable lengths are offered: 6 ft at $81, 12 ft at $93, 20 ft at $111 and 50 ft at $265. Choose the length deliberately rather than defaulting to the shortest, since a cable that has to be extended later is more trouble than the right one now. The anti-rotation hardware is the other thing to settle at the same time.
How does temperature affect a CLP reading?
The compensated range is 60° to 160°F with safe limits from −65° to 200°F. Output drift is 0.0085% of load per °F and zero drift is 0.003% of rated output per °F. That zero figure is better than most of our range while the span figure is slightly wider, which suits the application: an outdoor pin left in place through a full year sees a very large temperature swing, and a stable zero is what keeps a monitoring installation honest across it. Where the measurement matters, re-zero with the joint unloaded and at working temperature.
Can the CLP be calibrated in tension and compression?
A load pin does not work in those terms — it responds to shear across the pin, and the load reaches it through the bearing surfaces of your joint, whichever way the assembly is being pulled. What matters far more than direction is that the calibration reflects the loading arrangement the pin will actually see. Where the results have to be defensible, tell us about the joint at the point of order so the calibration can be set up to match it.
Questions From The Field
My readings are consistently low but perfectly steady. What should I check?
Check rotation first. If the pin has turned in its bore, the sensing plane no longer lines up with the load, and what you get is a reading reduced by a consistent proportion — stable, repeatable and wrong, which is much harder to spot than something erratic. Confirm the anti-rotation hardware is present, correctly fitted and actually restraining the pin rather than merely being there. After that, look at whether the load is arriving where the pin expects it: a spacer left out or a link narrower than intended will shift the bearing positions away from the shear planes.
Can I fit a load pin to a joint that came from somewhere else?
Only if the dimensions correspond, and it is worth being careful here because a pin that physically slides in is not necessarily a pin that reads correctly. The bore diameter has to suit, and so do the ear thicknesses and the centre width, because those set where force enters relative to the shear planes. Measure the joint properly, send us the numbers, and let us confirm before you order. A pin that fits mechanically but is loaded in the wrong places will give you a number that looks entirely plausible.
Does the strength of my clevis affect the reading?
Yes, and it is one of the least expected error sources on this product. The bearing surfaces of the clevis and the link have to be hard and strong enough not to deform at working load. Installation guidance for load pins states plainly that at high loads the yield stress in the clevis metal can cause measurement errors that are nothing to do with the pin — the ears spread or the bore ovalises, the load redistributes along the pin, and the reading changes. If you are approaching the top of your range and the numbers are drifting, inspect the joint before suspecting the sensor.
The smallest models do not list a key. How is rotation prevented on those?
On the smaller pins the arrangement is different, which is why a snap ring groove is provided rather than a key. Published guidance for pins under two inches notes that a keeper plate restrains rotation in one direction only and needs a retaining ring or nut alongside it. In practice that means the anti-rotation and the axial retention are two separate jobs on small pins, and both have to be arranged. Tell us the joint and we will specify what is needed — this is exactly the detail that gets discovered on installation day if it is not settled beforehand.
Can I hammer the pin into place if the fit is tight?
No. Guidance for this product class is explicit that no axial force should be applied to the pin during installation or in use, and driving one in with a hammer is precisely that. If the pin will not slide in, something is wrong with the fit, the alignment or the bore condition, and forcing it risks damaging a sensing element you cannot inspect. Ease the joint into alignment, check the bore for burrs or corrosion, and confirm the clearance is what it should be for the diameter. If it still will not enter, call us before you reach for anything heavier.
Can I rely on a load pin as part of a safety system?
It can be a valuable input to one, and load monitoring on lifting and rigging equipment is a listed use. The distinction to keep hold of is that our published figures describe how well the pin measures, not how much it is rated to lift — a load pin is an instrument, not certified rigging hardware, and it is replacing a component whose structural rating is a separate matter entirely. Where a pin is going into a lifting or mooring arrangement, the design of that arrangement needs to be settled by whoever is responsible for it, with the pin's dimensions and capacity supplied as an input. Talk to us about the sensor and to them about the joint.
How should the cable be routed on a pin fitted to something that moves?
Carefully, because this is where installations most often fail in service. The pin is fitted into a joint that rotates, swings or articulates, so the cable must be routed and anchored so that motion is never taken by the connector. Secure it close to the pin so the connector carries no load, allow a service loop with enough slack for the full range of movement, avoid tight bends at the exit, and protect it mechanically where anything can chafe or crush it. On a moving assembly the cable is usually the shortest-lived part, and most of that is preventable at installation.
What maintenance does an installed load pin need?
Four things, at whatever interval suits the duty. Confirm the anti-rotation hardware is still doing its job, since a fastener that has worked loose lets the pin turn and quietly reduces the reading. Inspect the bore and the bearing surfaces of the joint for wear, ovalisation or spreading, which change how load reaches the pin. Check the cable and connector for damage, corrosion and strain. And compare the unloaded reading against the zero balance on the certificate — a growing offset is the earliest useful sign that something in the joint or the sensor has changed. Recalibrate annually, or sooner after any suspected overload.