Most guides on how to choose a constant tension hose clamp stop at “pick one that fits the hose.” That is the easy part. The parts that decide whether the joint stays dry for years are where the hose OD sits inside the clamp’s range, whether you need the standard or heavy-duty build, which material suits the environment, and whether the band will get along with the hose wall. This post is laid out as a worksheet: seven steps, each with a short prompt you can fill in for your own joint.
We are not going to explain again how the Belleville washer stack works or what a hose goes through over a heat cycle. That is covered in our constant tension vs standard hose clamp comparison. If you are chasing a coolant leak and are not sure the clamp is to blame, start with the symptom guide in our radiator hose clamp article. This one assumes you already know you want a spring-loaded clamp and need to buy the right one.
How to use this constant tension hose clamp worksheet
Print the page, or copy the checklist at the end into your job sheet. For each hose joint, write down:
- The machine or vehicle, and the hose position (for example “upper radiator, engine side”).
- Your answer to each step’s prompt.
- The OTE part number you land on, and any OEM number it replaces.
Step 1: Confirm the joint really needs a constant tension clamp
A constant tension hose clamp costs more than a plain worm gear clamp and needs a little more room. It earns that only when the joint changes temperature enough to make the hose and the fitting move. Answer yes or no to each line below.
- Does the fluid or air in the hose get hot in service and then cool right down when the machine stops?
- Is the hose rubber or another elastomer that can take a set and thin out under the band over time?
- Is the fitting aluminium, plastic or a different metal from the clamp, so it grows and shrinks at a different rate?
- Is the joint under pressure or vacuum, so a small loss of grip turns into a seep or a pull-off?
- Has this joint needed re-tightening before, or shown crust or weeping after the engine sat overnight?
Two or more yeses, and one of them is the first line, means a constant tension hose clamp is a good fit. Typical candidates are radiator, heater, bypass and oil cooler hoses, plus smaller charge air cooler hoses.
If every answer is no, for example a cold water line, a vent, or a low-pressure suction hose at ambient temperature, a standard perforated worm gear clamp does the job. If the hose is very large or carries heavy boost, a spring-loaded T-bolt clamp may suit better than any band-and-screw design; we come back to that in Step 3.
Worksheet prompt 1: Joint name ________. Heat cycling? Y / N. Number of yeses ____. Decision: constant tension / standard worm / T-bolt.
Step 2: Measure the installed hose OD and size for mid travel
Sizing is where most constant tension hose clamp installs go wrong, and the reason is specific to spring clamps. A plain worm clamp only needs to close down onto the hose. A constant torque clamp also needs spare movement in its washer stack and band so it can follow the hose as it grows and shrinks. A clamp pulled right down to the bottom of its range, or opened right to the top, leaves little of that movement in reserve.
Measure the right thing
You need the outside diameter of the hose where the band will sit, with the hose pushed fully onto its fitting. That number is larger than the hose’s nominal ID, and by an amount that changes with wall thickness, reinforcement plies and brand. Two “2 inch” coolant hoses from different makers can differ in OD by several millimetres. Do not size from the hose’s printed ID.
The cleanest way is with calipers across the hose over the fitting bead, measured twice at 90 degrees, then averaged. If you cannot get calipers in, wrap a strip of paper around the hose, mark the overlap, lay it flat and divide the length by pi (3.1416). The result is the OD.
Hot vs cold: which OD to write down
Measure with the system cold and depressurised, which is how the clamp will be installed. The hose will be slightly larger when it is hot and pressurised, and it will lose some wall thickness under the band over months of service. The clamp needs room both ways, so the target is the middle of the range rather than the edge.
A practical rule we use: aim for the installed OD to fall in the middle half of the clamp’s stated range. If the range is 2.06–3.00 in, the comfortable window is roughly 2.30–2.77 in. If your OD is right on the line between two clamps, pick the one that puts you nearer its centre. For soft, thick-walled hose, favour the clamp where your OD sits in the upper half, leaving more closing travel.
Constant tension clamp size chart: standard range
The table below lists every standard OneTouch Exim constant torque clamp with its range in inches, the millimetre equivalent, the span of the range, and the mid-travel window we suggest. For a full inch-to-mm list covering all clamp families, see our hose clamp size chart in mm and inches.
| OTE part no. | Range (in) | Range (mm) | Span | Mid-travel target OD |
|---|---|---|---|---|
| OTE-4CT0010 | 0.56–1.06 | 14–27 | 0.50 in (13 mm) | 0.69–0.94 in (17–24 mm) |
| OTE-4CT0012 | 0.69–1.25 | 18–32 | 0.56 in (14 mm) | 0.83–1.11 in (21–28 mm) |
| OTE-4CT0016 | 0.81–1.50 | 21–38 | 0.69 in (18 mm) | 0.98–1.33 in (25–34 mm) |
| OTE-4CT0020 | 0.81–1.75 | 21–44 | 0.94 in (24 mm) | 1.04–1.52 in (27–38 mm) |
| OTE-4CT0024 | 1.06–2.00 | 27–51 | 0.94 in (24 mm) | 1.29–1.77 in (33–45 mm) |
| OTE-4CT0028 | 1.31–2.25 | 33–57 | 0.94 in (24 mm) | 1.54–2.02 in (39–51 mm) |
| OTE-4CT0032 | 1.56–2.50 | 40–64 | 0.94 in (24 mm) | 1.79–2.27 in (46–58 mm) |
| OTE-4CT0036 | 1.81–2.75 | 46–70 | 0.94 in (24 mm) | 2.04–2.52 in (52–64 mm) |
| OTE-4CT0040 | 2.06–3.00 | 52–76 | 0.94 in (24 mm) | 2.29–2.77 in (58–70 mm) |
| OTE-4CT0044 | 2.31–3.25 | 59–83 | 0.94 in (24 mm) | 2.54–3.02 in (65–77 mm) |
| OTE-4CT0048 | 2.56–3.50 | 65–89 | 0.94 in (24 mm) | 2.79–3.27 in (71–83 mm) |
The smallest size, the 0.56–1.06 in constant torque clamp (OTE-4CT0010), suits heater and bypass hoses. From 4CT0024 upward the ranges step by 0.25 in and overlap heavily, so almost any OD from 1.3 to 3.2 in sits in the mid window of at least one size.
Constant torque hose clamp sizes: heavy-duty range
| OTE part no. | Range (in) | Range (mm) | Span | Mid-travel target OD |
|---|---|---|---|---|
| OTE-4CT175L / OTE-4CT175S | 1.00–1.75 | 25–44 | 0.75 in (19 mm) | 1.19–1.56 in (30–40 mm) |
| OTE-4CT200L / OTE-4CT200S | 1.25–2.13 | 32–54 | 0.88 in (22 mm) | 1.47–1.91 in (37–49 mm) |
| OTE-4CT250L / OTE-4CT250S | 1.75–2.63 | 44–67 | 0.88 in (22 mm) | 1.97–2.41 in (50–61 mm) |
| OTE-4CT300L / OTE-4CT300S | 2.25–3.13 | 57–80 | 0.88 in (22 mm) | 2.47–2.91 in (63–74 mm) |
| OTE-4CT350L / OTE-4CT350S | 2.75–3.63 | 70–92 | 0.88 in (22 mm) | 2.97–3.41 in (75–87 mm) |
| OTE-4CT400L / OTE-4CT400S | 3.25–4.13 | 83–105 | 0.88 in (22 mm) | 3.47–3.91 in (88–99 mm) |
| OTE-4CT450L / OTE-4CT450S | 3.75–4.63 | 95–118 | 0.88 in (22 mm) | 3.97–4.41 in (101–112 mm) |
| OTE-4CT500L / OTE-4CT500S | 4.25–5.13 | 108–130 | 0.88 in (22 mm) | 4.47–4.91 in (114–125 mm) |
| OTE-4CT550L / OTE-4CT550S | 4.75–5.63 | 121–143 | 0.88 in (22 mm) | 4.97–5.41 in (126–137 mm) |
| OTE-4CT600L / OTE-4CT600S | 5.25–6.13 | 133–156 | 0.88 in (22 mm) | 5.47–5.91 in (139–150 mm) |
| OTE-4CT650L / OTE-4CT650S | 5.75–6.63 | 146–168 | 0.88 in (22 mm) | 5.97–6.41 in (152–163 mm) |
| OTE-4CT700L / OTE-4CT700S | 6.25–7.13 | 159–181 | 0.88 in (22 mm) | 6.47–6.91 in (164–176 mm) |
| OTE-4CT750L / OTE-4CT750S | 6.75–7.63 | 171–194 | 0.88 in (22 mm) | 6.97–7.41 in (177–188 mm) |
| OTE-4CT800L / OTE-4CT800S | 7.25–8.13 | 184–207 | 0.88 in (22 mm) | 7.47–7.91 in (190–201 mm) |
| OTE-4CT850L / OTE-4CT850S | 7.75–8.63 | 197–219 | 0.88 in (22 mm) | 7.97–8.41 in (202–214 mm) |
The heavy-duty sizes overlap generously and run up to 8.63 in, covering big truck radiator outlets, charge air hoses and industrial coolant headers that the standard series does not reach.
Worksheet prompt 2: Installed OD, cold ______ in / ______ mm. Measured with: calipers / paper strip. Candidate sizes ________. Size that puts OD nearest centre ________.
Step 3: Standard or heavy-duty constant torque clamp?
Once you know the size, the overlap zone between about 1 in and 3.5 in gives you a choice: both the standard 4CT00xx series and the heavy-duty 4CTxxxL series cover it. Above 3.5 in, only the heavy-duty series applies.
The heavy duty constant torque clamp is a heavier build than the standard version, and this class usually has a wider band that spreads load over more hose, which helps on large diameters. Check band width and screw details on the product page before you commit.
Choose heavy-duty when
- The hose OD is above 3.5 in. There is no standard option.
- It is a heavy truck, bus, off-highway or genset coolant joint, where hoses are thick-walled, reinforced and vibrate for long hours.
- It is a charge air cooler (CAC) hose of moderate size, where boost pressure and heat cycles work the joint at the same time.
- The OEM fitted a heavy-duty constant torque clamp there. Match the original class, even if a standard one would fit.
Standard is usually enough when
- It is a light vehicle, van or small engine cooling hose under about 3 in OD.
- Heater hoses, bypass hoses and small oil cooler lines on any size of engine.
- Space around the joint is tight and a wider band would ride off the bead or touch a neighbouring part.
When neither is the answer
On large-diameter boost hoses that see high pressure, a spring-loaded T-bolt clamp gives a solid band with 360-degree contact and a spring on the bolt. These have narrow ranges, so measurement has to be precise.
Two worked examples. A pickup’s upper radiator hose measures 1.72 in OD on the neck. The standard OTE-4CT0024 (1.06–2.00 in) places it in the upper half of its range, and the HD 4CT200L (1.25–2.13 in) puts it near the centre too. For a pickup, standard is fine. A Class 8 truck lower radiator hose measures 2.70 in OD. The heavy-duty OTE-4CT300L (2.25–3.13 in) puts it right in the middle, and the joint class calls for heavy-duty anyway.
Worksheet prompt 3: Vehicle/equipment class ________. OEM clamp type ________. Choice: standard 4CT00xx / heavy-duty 4CTxxxL / spring T-bolt.
Step 4: Pick the material, standard build or stainless constant tension clamp
In the OneTouch Exim heavy-duty range, each size comes in two versions. The part number ends in L or S. Going by the catalogue naming, the L models are the standard build and the S models are all stainless, meaning the screw, housing and washers as well as the band. So OTE-4CT400L and OTE-4CT400S cover the same 3.25–4.13 in range in the two materials. Confirm the exact material of each component on the product page or with our team before you order, especially if you are writing a specification.
Why it matters: on many clamps the band is stainless but the screw and washers are plated carbon steel. Where salt, washdown chemicals or constant moisture reach the clamp, those plated parts rust first, and rusted washers stop springing properly.
Choose all-stainless (S) when the clamp lives in
- Road-salt regions, coastal fleets and anything near seawater.
- Equipment that is pressure-washed often: refuse trucks, food plant gensets, agricultural machinery.
- Underbody or low-mounted positions that collect spray and mud.
- Machines stored outdoors for long periods between use, such as standby generators and seasonal plant.
For a dry, under-hood position on a road truck, the L version is a sensible choice and keeps cost down. If you are weighing grades of stainless more generally, our 304 vs 316 stainless steel comparison explains where the extra molybdenum in 316 earns its price. Ask us which grade a particular clamp uses if your specification calls for one.
The standard 4CT00xx series is listed as a single version per size. If you need an all-stainless clamp below 1 in OD, raise it when you request a quote so we can confirm what is available.
Worksheet prompt 4: Exposure: dry / damp / salt / washdown. Version: L (standard) / S (all-stainless). Material confirmed on product page: Y / N.
Step 5: Check hose type compatibility
The constant tension hose clamp was developed around rubber hoses that take a set, and EPDM or similar coolant hose is still where they work best. The hose wall has some give, the band beds in slightly, and the spring takes up the rest.
Rubber hose (EPDM, nitrile, reinforced)
Rubber hoses that heat-cycle tend to lose wall thickness under the band as the compound slowly flows. In materials terms this is creep, often called cold flow in hose work. This is exactly the condition a constant torque clamp is made for. Any band style generally works on rubber, though for soft or thin-wall hose it is still worth checking the band edges are smooth and rolled.
Silicone hose
Silicone shows cold flow readily, so a spring clamp makes sense in principle, but slots in a perforated band can press into and cut its soft outer layer. Before fitting any constant tension clamp to silicone:
- Check the band design on the product page. Look for a band where the slots do not face the hose, or one with a smooth inner surface or liner.
- Check whether the hose maker allows worm-type clamps at all, and what clamp they recommend.
- Do not overtighten. Silicone needs less force to seal than rubber, and excessive load shows up quickly as bulging at the band edges.
If the band design does not suit, a lined hose clamp or a T-bolt with a solid band are the alternatives. The full reasoning, with sizes, is in our guide to the best hose clamps for silicone hoses.
For stiff thermoplastic hose, follow the hose maker’s fitting instructions; many such lines are designed around a specific clamp or crimped fitting.
Worksheet prompt 5: Hose material ________. Hose maker’s clamp guidance checked: Y / N. Band surface OK for this hose: Y / N / need lined clamp.
Step 6: Plan the constant tension clamp installation and access
A good clamp fitted badly still leaks. Spend two minutes on the joint before you order, because access can change which size or style you buy.
Screw orientation
The Belleville washer stack makes the screw housing taller than on a plain worm clamp. Look at where the screw head will point once the clamp is on. It needs:
- A straight line for a nut driver or socket, with no bracket, pipe or fan shroud in the way.
- Clearance from moving parts: belts, fan blades, steering links and suspension travel.
- A position where you can see the washer stack, so the fitter can check it during tightening and the next technician can check it at service.
If every orientation is blocked, note it. You may need a different routing or a T-bolt clamp, whose bolt takes a different tool angle.
Tools
Use a nut driver or a socket on a torque-limiting driver, not a flat screwdriver. Check the hex size on the product page and have the right driver in the kit before the job starts.
How tight: follow the maker’s washer-stack instruction
We are deliberately not giving a torque number here. Constant tension clamps are tightened by the condition of the washer stack, and makers word the instruction differently: some say tighten until the stack is just flat, some say flat and then back off a set amount, some give a torque window as well. Use the instruction that comes with the clamp you buy, and do not copy a figure from another brand or from a plain worm clamp. Our guide on how tight a hose clamp should be gives the wider context.
Installation habits that pay off
- Install cold, on a clean, dry fitting.
- Position the band fully on the hose, behind the bead, with a small margin from the hose end. Do not let the band edge sit on the bead itself.
- Open the clamp enough to slide it on without forcing the band past its range.
- Do not “re-tighten” a warm constant tension clamp to stop a seep. If it leaks with the stack set correctly, the size, the hose or the fitting is the problem.
Worksheet prompt 6: Screw direction ________. Tool access clear: Y / N. Driver size ________. Tightening per maker: flat / flat and back off / torque value ________.
Step 7: Order the right constant torque clamp
Match OEM and aftermarket numbers
If you are replacing an existing clamp, the old part number is the fastest route to the right size. OneTouch Exim product pages list interchange numbers from brands such as Norma, Breeze, Gates and Automann, and our clamp cross-reference tool searches more than 3,000 OEM and aftermarket numbers across the range. Those names and numbers are listed for reference and interchange only; OneTouch Exim has no affiliation with those companies.
Still measure. A replacement hose from a different supplier can change the OD enough to push you into the next size.
Quantities
- Count both ends of every hose. A straight radiator hose has two joints; a branched hose may have three or four.
- Some high-pressure or long-bead joints use two clamps side by side. Check the OEM layout.
- Add spares for clamps damaged during removal and for the next service, especially on sizes common across your fleet.
Packaging and shipping
OneTouch Exim quotes per order, from single units to export cartons, and ships worldwide. If you need clamps bagged by kit (for example one bag per engine with the right mix of sizes), labelled with your own part numbers, or packed for a particular warehouse system, say so when you ask for a quote.
A worked constant torque clamp for coolant hose order
Here is how one completed worksheet line might read for a fleet of ten medium-duty trucks, all based on real catalogue ranges but with example hose measurements:
| Joint | Measured OD | Choice | Why | Qty (10 trucks + spares) |
|---|---|---|---|---|
| Upper radiator, both ends | 2.40 in (61 mm) | OTE-4CT0040 | Near centre of 2.06–3.00 in; dry engine bay | 20 + 4 |
| Lower radiator, both ends | 2.65 in (67 mm) | OTE-4CT300L | Centre of 2.25–3.13 in; heavy, thick-wall hose | 20 + 4 |
| Heater supply and return | 1.00 in (25 mm) | OTE-4CT0016 | Inside 0.81–1.50 in mid window | 40 + 6 |
| CAC hose, cold side | 4.10 in (104 mm) | OTE-4CT450S | Mid of 3.75–4.63 in; front-mounted, salt exposure | 20 + 4 |
Note the CAC line: a front-mounted charge air cooler in a salted region gets spray all winter, so it goes to the all-stainless S version, while the engine-bay joints stay on standard builds. For the upper radiator, the standard OTE-4CT0040 constant torque clamp is adequate for medium-duty use, but a fleet running long-haul in hot climates might step up to the heavy-duty 4CT300L at both radiator joints and stock one part number instead of two. That is the kind of judgement call the worksheet makes visible.
Worksheet prompt 7: OTE part no. ________. Replaces OEM/aftermarket no. ________. Qty per unit ____ × units ____ + spares ____. Packaging notes ________.
Printable constant tension hose clamp selection checklist
Copy this list into your job card or purchase request. Tick each line for every joint.
- Joint heat-cycles in service (hot running, cold at rest)? If no, consider a standard worm gear clamp.
- Installed hose OD measured cold, on the fitting, with calipers or a paper strip: ______ in / ______ mm.
- Clamp chosen puts that OD in the middle half of its range.
- Duty class chosen: standard 4CT00xx (up to 3.50 in) or heavy-duty 4CTxxx (1.00–8.63 in) based on equipment and OEM fit.
- Material chosen: L (standard) or S (all-stainless), with exposure noted and component materials confirmed on the product page.
- Hose material checked against band design; lined or T-bolt alternative noted if needed.
- Screw orientation planned, tool access clear, driver size noted.
- Tightening method copied from the clamp maker’s instruction (washer stack condition and any torque window).
- OEM/aftermarket number cross-referenced and still checked against measured OD.
- Quantity counts every joint, plus spares; packaging and labelling needs stated on the quote request.
Constant tension clamp selection: FAQs
What size constant tension clamp do I need for a 2 inch hose?
It depends on the hose’s outside diameter, not the 2 inch inside diameter. A 2 inch ID coolant hose often measures somewhere around 2.4–2.7 in OD, but wall thickness varies by maker. Measure the OD on the fitting, then pick the clamp that puts it near the middle of its range. For example, 2.5 in OD sits well in OTE-4CT0040 (2.06–3.00 in) or HD OTE-4CT300L (2.25–3.13 in).
What do the L and S suffixes mean on heavy-duty constant torque clamps?
In the OneTouch Exim heavy-duty range, each size is offered as an L model and an S model with the same diameter range. Going by the catalogue naming, L is the standard build and S is the all-stainless build. Check the component materials on the individual product page, or ask our team, before you specify one, especially for salt, washdown or marine-adjacent use.
Can I use one clamp size across several different hoses to simplify stock?
Often yes, because ranges overlap. If several hose ODs all fall inside the middle half of one clamp’s range, standardising on that clamp is sensible. Avoid stretching one size to cover an OD near either end of its range just to save a part number. The spring needs travel in both directions, and a clamp at its limit loses much of the benefit you paid for.
Is a heavy-duty constant torque clamp always better than a standard one?
No. Heavy-duty clamps are bulkier and cost more. On small hoses, light vehicles and tight engine bays, a standard constant tension clamp seals well and fits where a heavier one might foul nearby parts. Choose heavy-duty for large diameters, thick reinforced truck and genset hoses, charge air hoses, or wherever the original equipment used a heavy-duty clamp.
How do I find the OneTouch equivalent of a Norma, Breeze or Gates clamp?
Enter the part number into the OneTouch Exim cross-reference tool, which covers more than 3,000 OEM and aftermarket numbers, or check the interchange list on each product page. Then measure the hose OD to confirm the match, since replacement hoses can differ from the original. Brand names are listed for interchange reference only, with no affiliation implied.
Do I need a special tool to fit a constant tension clamp?
No special tool, but use a nut driver or socket of the right hex size rather than a screwdriver, ideally on a torque-limiting driver. Tighten according to the clamp maker’s instruction about the washer stack, which may be “just flat”, “flat then back off” or a stated torque range.
Send us your completed worksheet
If you have filled in the worksheet, you already know how to choose a constant tension hose clamp for each joint. Send your measured ODs, the equipment, the exposure and any OEM numbers, and we will confirm the matching constant torque clamp sizes, standard or heavy-duty, L or S, with a quote for single units or export cartons. You can also browse the full constant tension clamp range first, or reach us on WhatsApp at +91-7838759114.