Every spring the same line turns up on commissioning lists: “4 x 1-1/2 inch stainless hose clamps, wet exhaust.” The owner reads “1-1/2 in” on the hose, buys clamps with the same number on the packet, and on the day the band either won’t go round the hose or goes round with the screw jammed at the end of its travel. This guide gives you a marine hose clamp size chart and a system-by-system way to measure on the boat, so the clamps you order fit first time.
The mix-up comes from two different numbers. Marine hose is named by its inside diameter, because that is what has to match the spigot. A clamp is named by the outside diameter it can grip, because the band wraps the outer wall. Wet exhaust hose has a thick wall: Trident lists its 1-1/2 in ID 200 and 250 series exhaust hose at 1.97 in OD, almost half an inch more than the number on the packet. A clamp sold as “up to 1-1/2 in” never had a chance.
Marine hose clamp size chart: SAE numbers in inches and mm
Most worm gear clamps sold for boats carry an SAE size number from the series used in SAE J1508, Hose Clamp Specifications. The number is a code, not a diameter, so look it up rather than trying to decode it. The ranges below for 1/2 in band clamps were cross-checked against a published worm drive clamp specification sheet, a marine distributor’s 316 clamp listing and the OneTouch catalog. Millimeter figures are our conversions at 25.4 mm per inch, rounded.
| SAE size | Range (in, fraction) | Range (in, decimal) | Range (mm) | Where it turns up aboard |
|---|---|---|---|---|
| 4 | 1/4 – 5/8 | 0.25 – 0.63 | 6 – 16 | Small vent and drain tubing (often a mini band) |
| 6 | 7/16 – 25/32 | 0.44 – 0.78 | 11 – 20 | 1/4–3/8 in fuel hose |
| 8 | 1/2 – 29/32 | 0.50 – 0.91 | 13 – 23 | 1/2 in fuel, 5/8 in freshwater |
| 10 | 9/16 – 1-1/16 | 0.56 – 1.06 | 14 – 27 | 3/4 in freshwater, 5/8 in vent |
| 12 | 11/16 – 1-1/4 | 0.69 – 1.25 | 17 – 32 | Washdown, small raw water |
| 16 | 13/16 – 1-1/2 | 0.81 – 1.50 | 21 – 38 | 3/4 in raw water intake |
| 20 | 13/16 – 1-3/4 | 0.81 – 1.75 | 21 – 44 | Bilge discharge, 1 in sanitation |
| 24 | 1-1/16 – 2 | 1.06 – 2.00 | 27 – 51 | 1 in wire intake hose |
| 28 | 1-5/16 – 2-1/4 | 1.31 – 2.25 | 33 – 57 | 1-1/4 in raw water |
| 32 | 1-9/16 – 2-1/2 | 1.56 – 2.50 | 40 – 64 | 1-1/2 in exhaust, sanitation, fill, drains |
| 36 | 1-13/16 – 2-3/4 | 1.81 – 2.75 | 46 – 70 | 1-3/4 to 1-7/8 in hose |
| 40 | 2-1/16 – 3 | 2.06 – 3.00 | 52 – 76 | 2 in exhaust and fill |
| 44 | 2-5/16 – 3-1/4 | 2.31 – 3.25 | 59 – 83 | 2-1/4 in exhaust |
| 48 | 2-9/16 – 3-1/2 | 2.56 – 3.50 | 65 – 89 | 2-1/2 in exhaust |
| 52 | 2-13/16 – 3-3/4 | 2.81 – 3.75 | 71 – 95 | 2-3/4 in exhaust |
| 56 | 3-1/16 – 4 | 3.06 – 4.00 | 78 – 102 | 3 in exhaust |
| 60 | 3-5/16 – 4-1/4 | 3.31 – 4.25 | 84 – 108 | 3-1/4 in exhaust |
| 64 | 3-9/16 – 4-1/2 | 3.56 – 4.50 | 90 – 114 | 3-1/2 in exhaust |
| 72 | 4-1/16 – 5 | 4.06 – 5.00 | 103 – 127 | 4 in exhaust |
| 80 | 4-9/16 – 5-1/2 | 4.56 – 5.50 | 116 – 140 | 4-1/2 in exhaust |
| 88 | approx. 5-1/4 – 6 | 5.27 – 6.00 | 134 – 152 | 5 in exhaust |
| 96 | 5-5/8 – 6-1/2 | 5.62 – 6.50 | 143 – 165 | Large exhaust (check OD) |
| 104 | 6-9/16 – 7 | 6.56 – 7.00 | 167 – 178 | Large exhaust and intake |
Two things catch people out. The ranges overlap heavily, so a 2.00 in OD sits inside SAE 24, 28 and 32, and choosing between them is the real decision. And SAE 16 and 20 start at the same 13/16 in; they differ only in reach. For the full non-marine chart with a metric-first lookup, see our hose clamp size chart in mm and inches; for the history of the numbering, our SAE J1508 explainer.
Boat hose clamp sizes by onboard system
This second half of the marine hose clamp size chart starts from the hose instead. The OD figures come from published Trident spec sheets (100, 200, 250 and 252V exhaust and water hose, 101/102 sanitation, 327 A2 fill, 365 A1 fuel, 147 bilge and 162 freshwater hose). Other brands differ, and two hoses with the same ID can have very different walls, so read the OD printed on your hose or its data sheet.
| System | Typical hose ID | Approx. OD (loose) | Suggested SAE size | Clamps per end |
|---|---|---|---|---|
| Raw water intake | 3/4 in | 1.15 – 1.25 in | 16 (20 at the high end) | Two if the tail allows; one is acceptable |
| Raw water intake | 1 in | 1.50 – 1.57 in | 24 | Two if the tail allows |
| Raw water intake | 1-1/4 in | approx. 1.75 in | 28 | Two if the tail allows |
| Wet exhaust | 1-1/2 in | 1.97 – 2.00 in | 32 | Two (required) |
| Wet exhaust | 2 in | 2.50 – 2.60 in | 40 | Two (required) |
| Wet exhaust | 2-1/2 in | 3.06 – 3.10 in | 48 | Two (required) |
| Wet exhaust | 3 in | approx. 3.61 in | 56 | Two (required) |
| Wet exhaust | 4 in | 4.63 – 4.70 in | 72 | Two (required) |
| Cockpit and deck drains | 1-1/2 in | 1.97 – 2.00 in | 32 | Two at the through-hull if it fits |
| Bilge pump discharge | 1-1/8 in PVC | approx. 1.39 in | 20, 24 or lined | One is common |
| Sanitation | 1 in | approx. 1.42 in | 20 or 24 | Two on smooth spigots |
| Sanitation | 1-1/2 in | approx. 2.00 in | 32 | Two on smooth spigots |
| Fuel fill | 1-1/2 in | approx. 2.00 in | 32 | Two (required) |
| Fuel vent | 5/8 in | approx. 1.00 in | 10 or 12 | Per hose and fitting maker |
| Freshwater PVC | 5/8 / 3/4 in | 0.74 / 0.88 in | 8 / 10 | One |
Why the screw should land mid-range when you double-clamp
Every pick above puts the measured OD roughly 40 to 65 percent of the way through the clamp’s range. On a boat that matters more than usual, because paired clamps don’t sit on the same diameter. The inner band rides over the barbs or the fullest part of the spigot; the outer one sits nearer the hose end, where the spigot may taper. Choose a size that only just reaches and one clamp closes while the other won’t. Choose one that starts near your OD and the screw runs out of thread before the band bites. Mid-range means one part number works in both positions, with thread left for re-tightening after the first heat cycles.
Take the opening example. A 1.97 in exhaust hose sits about 43 percent into an SAE 32 (1.56–2.50 in), 70 percent into an SAE 28, and 97 percent into an SAE 24. All three “fit” on paper. Only one is a sound choice.
Walk the boat: how to measure each system
The best time to build a clamp list is at haul-out, hull on stands, hatches open. Start at the seacocks and work up and aft with a notebook, masking tape and a pen. Tag every joint (“RW-1 seacock tail”, “EX-3 muffler inlet”) and record four things: the printed hose ID, the installed OD, the clear spigot length, and how many clamps are on it now.
1. Seacocks and raw water intake
Measure the hose OD over the seacock tailpiece, then at the strainer and the raw water pump inlet. These hoses are usually 3/4 to 1-1/4 in ID and wire-reinforced against suction collapse. Read the hose where it covers the tail, not the loose loop: a hose on a fitting grows by about twice the difference between spigot OD and hose ID, which on a tight fit can push you into the next size.
Watch for short bronze tails. Practical Sailor’s summary of ABYC practice is to keep clamps at least 1/4 in from the spigot end and never overlap them; if that leaves room for one band, fit one good clamp, not two crowded ones. ABYC accepts a single clamp on a raw water intake. Size: a 3/4 in hose at about 1.15 in OD sits mid-range in an SAE 16. A 1 in wire hose at 1.5 in is better in an SAE 24 than an SAE 20, where it is already three-quarters closed.
2. Engine cooling hoses
Measure both circuits on a heat-exchanger engine: raw water (pump, heat exchanger, injection elbow) and freshwater coolant (engine, exchanger, calorifier loop). Heat exchanger caps and pump spigots are often short and beaded rather than barbed, so measure just behind the bead where the band will sit.
Watch for thinner walls. Molded coolant hose is often close to ID plus 1/4 in, so don’t copy an exhaust clamp size onto a coolant hose of the same ID. Calorifier loops are frequently 5/8 in heater hose needing something near an SAE 10. These joints cycle hot and cold, which is why our guide to choosing a marine hose clamp by duty leans toward constant torque clamps on the coolant side. Size: stay mid-range so you can take up compression set after the first runs; an oversize clamp nearly closed leaves a band tail that snags hands and wiring.
3. Wet exhaust
Measure over the injection elbow outlet, both muffler connections and the hull outlet, at both clamp positions, since cast elbows can taper. This is where the opening mistake happens. From Trident’s published IDs and ODs, walls work out at about 0.235 in for 1-1/2 in hose, rising to roughly 0.3 in at 3 to 4 in.
Watch for wire-reinforced hose. Trident’s 100 and 250 series carry a steel helix between plies, so the wall won’t squeeze down; extra torque only loads the screw and cuts the cover. Hardwall hose can also stop short of full engagement, leaving the clamps over unsupported hose. Warm the end in hot water, lubricate with soapy water, push it fully home, then measure. ABYC guidance, summarized on the ABYC hose clamp page, calls for two non-overlapping clamps at each end of every exhaust connection, and Practical Sailor adds all-stainless construction and at least 1/2 in bands.
Size: 1-1/2 in exhaust at 1.97 in takes an SAE 32; 2 in at 2.50 in sits at 47 percent of an SAE 40; 2-1/2 in at about 3.06 in suits an SAE 48 better than an SAE 44, which would be 80 percent closed. Where yards fit T-bolts on larger exhaust, our notes on choosing an exhaust clamp apply; confirm the material of every part, nut included.
4. Cockpit and deck drains
Measure at the scupper fitting and the through-hull. Drains are commonly 1-1/2 in ID wire hose at around 2 in OD. The through-hull end matters most, since it is often at or below the heeled waterline, and it is usually reached by lying in a locker. A paper strip (method below) beats calipers held at arm’s length.
Watch for ovality. Drain hoses run in tight bends that pull the hose sideways on its spigot. Take two readings at right angles, size for the average, and make sure it still sits mid-range so the clamp can pull the hose round. Size: SAE 32 for a 2.0 in OD, doubled at the through-hull where the tail allows.
5. Bilge pump discharge
Measure at the pump outlet, any check valve and the hull fitting. Common sizes are 3/4 and 1-1/8 in ID PVC. Pump outlets are often short molded plastic with very little barb, so measure close to the pump body.
Watch for thin, soft walls. Trident’s 1-1/8 in heavy-wall vinyl lists at 1.39 in OD. A perforated band can bite soft PVC, and a plastic spigot cracks before the joint stops leaking, so this is the place for a lined clamp and a light hand; our sibling guide on tightening a hose clamp without over-torquing covers stopping points. Size: 1.39 in sits at about 62 percent of an SAE 20 and 35 percent of an SAE 24; either works, or a lined 1.06–2.00 in clamp if the hose is soft.
6. Sanitation hose clamp size
Measure at the toilet outlet, holding tank fittings, Y-valve, macerator and pump-out. The Trident 101/102 sanitation hose data sheet lists 1-1/2 in ID at 2.00 in OD, 1 in at 1.42 in, and 1-7/8 in at 2.38 in. Tank fittings are often smooth plastic spigots with no barbs, so measure where the clamp will sit, back from the end.
Watch for stiff hose that won’t seat. Helix-reinforced sanitation hose is notoriously hard to push on, and one that stops half an inch short leaves no room for a second clamp, which Practical Sailor’s reading of ABYC practice expects on smooth spigots. Size: 2.00 in lands at 47 percent of an SAE 32; 1.42 in suits an SAE 20 or 24; 2.38 in sits best in an SAE 36. Use matching clamps on each joint.
7. Fuel fill and vent
Measure the fill hose at the deck plate and tank inlet, and the vent at the tank and hull fitting. Trident’s 1-1/2 in Type A2 fill hose lists a 2 in OD; its 5/8 in A1 fuel hose lists 1.00 in. ABYC asks for hose ID to match fitting OD within a tolerance, so installed OD should stay close to the printed figure.
Watch for the rules. Fuel hose must be the USCG/ABYC-rated type for its job, and ABYC’s fuel standards call for at least two corrosion-resistant metal clamps of at least 1/2 in nominal width at each fill connection. ABYC also warns that some Type A and some wire- or mesh-reinforced hose is not meant to be clamped. Follow the hose maker and the applicable ABYC standard (H-24 gasoline, H-33 diesel) over any general chart. Size: SAE 32 for a 2 in OD fill hose; SAE 10 or 12 for a 1 in vent, whichever leaves the screw nearer mid-travel once measured in place.
8. Freshwater
Measure the clear reinforced PVC from tank to pump, accumulator and water heater, over the barb. Trident’s 162 series lists 5/8 in ID at 0.735 in OD and 3/4 in at 0.875 in. PEX with crimp or push-fit fittings takes no worm gear clamps, so leave it off the list.
Watch for warm-water creep. Hot water softens PVC, and a small clamp over-tightened on it splits the hose at the barb. One clamp is normal. Size: SAE 8 for 5/8 in hose (about 58 percent) and SAE 10 for 3/4 in (about 62 percent), after checking your own hose’s OD.
How to measure boat hose for a clamp without calipers
Calipers are awkward in a bilge: the jaws rarely sit square, you can’t read the scale with your head against a stringer, and above about 3 in the jaws only reach a chord. A paper strip measures circumference by feel, which is easier to get right in tight spaces.
- Cut a strip of thin paper or masking tape about 1/2 in wide and a few inches longer than the hose’s circumference.
- Wrap it once around the hose exactly where the clamp will sit, square to the hose, not spiraling.
- Pull it snug without stretching and mark the overlap with a fine pen line or pin prick.
- Lay it flat and measure from the end to the mark: that is the circumference.
- Divide by π (3.1416) for the outside diameter, and repeat at the second clamp position.
Worked example: hose clamp size for 1-1/2 inch exhaust hose
Your strip around a 1-1/2 in exhaust hose on the muffler inlet measures 6.30 in. Divided by 3.1416, that is 2.005 in, about 51 mm (a 160 mm strip gives the same: 160 ÷ 3.1416 = 50.9 mm). In an SAE 32, (2.005 − 1.56) ÷ (2.50 − 1.56) comes to about 47 percent: mid-range. The loose hose was listed at 1.97 in, so the spigot stretched it by about 0.035 in. Small here, but on a firmer fit that stretch can move you up a size.
You can also estimate before touching the hose: installed OD is roughly spigot OD plus twice the wall, where wall = (printed OD − ID) ÷ 2. A hypothetical 1.55 in spigot with a 0.235 in wall gives 1.55 + 0.47 = 2.02 in. Use that to shortlist, then confirm with the strip. Tool comparisons and an old-clamp lookup are in our guide on how to measure hose clamp size.
Rule of thumb from the bilge: if your reading falls in the last fifth of a clamp’s range at either end, move to the neighboring size. Overlapping ranges exist so you never have to accept an end-of-travel fit.
Checking there is room for two clamps
A correct size number is wasted if the second clamp has nowhere to go. For every joint marked “two” on your list, add up the length you need:
- Bands: two 1/2 in bands take 1 in.
- Gap: a visible space so the housings don’t touch, about 1/4 in in practice.
- End clearance: at least 1/4 in from the spigot end.
- Support: both bands on fully engaged hose, behind any bead.
That totals roughly 1-1/2 in of clean spigot for a pair of 1/2 in clamps (our arithmetic, not a published rule). With less, ABYC warns that a second clamp on a fitting designed for one can damage the hose and weaken the joint, so fit one correctly sized clamp or a longer fitting. Stagger the housings on paired clamps. The Practical Sailor article on clamps and barbs also reproduces ABYC’s clamp width by hose OD, with 1/2 in bands above 1-1/2 in OD.
Does a 316 hose clamp size chart differ? Material in brief
No. Size and grade are separate choices: a 316 SAE 32 covers the same range as a 304 or 301 SAE 32, so the marine hose clamp size chart above applies whatever you buy. Grade decides how long it survives salt water. Every part, screw included, must be stainless; 316 is preferred where a joint stays wet with seawater; a plated carbon steel screw does not belong aboard. The reasoning is in 304 vs 316 marine hose clamps.
Where OneTouch clamps fit on a boat, and where they don’t
OneTouch Exim makes band-type clamps in Noida, India, mainly for truck, diesel and industrial buyers. Part of the range suits boat work; part doesn’t.
- 4SS all-stainless worm gear: 301 band and housing, 410 stainless screw, 1/2 in band. The 4SS0032 all-stainless clamp (1.56–2.50 in) matches SAE 32 and covers most 1-1/2 in exhaust, sanitation, drain and fill hose; other sizes are under perforated worm gear clamps. Suited to splash and salt-air duty; not 316, so ask about permanently immersed joints.
- 4CL94xx lined all-stainless: a liner bridges the perforations, which helps on soft PVC and silicone. The 4CL9424 lined clamp (1.06–2.00 in) suits 1-1/8 in bilge discharge. The alloy grade isn’t published, so confirm it before marine use.
- 316: not a listed stock item. Ask, and we’ll confirm availability for your sizes and quantities.
- Standard 4SC worm gear: not for marine service. Its zinc-plated carbon steel screw rusts in salt air.
Replacing another brand’s clamps? Our clamp cross-reference tool converts 3,000+ OEM and competitor codes to the nearest OneTouch size; brand names are for identification only, and OneTouch is not affiliated with any of them. For which clamp type suits which job aboard, see the best hose clamps for marine and boat applications, and for why band style matters on soft hose, our sibling post on perforated vs solid band hose clamps.
Marine hose clamp sizes: common questions
What size hose clamp do I need for 1-1/2 inch exhaust hose?
Typical 1-1/2 in ID marine wet exhaust hose measures about 1.97 to 2.00 in outside, so an SAE 32 (roughly 1.56 to 2.50 in) is the usual pick and leaves the screw mid-travel. An SAE 28 closes too but runs much nearer its limit. Measure over the spigot first, because wall thickness varies by brand.
Do I size a boat hose clamp by hose ID or OD?
By OD, measured where the hose sits on its fitting. The printed ID tells you which spigot the hose fits; the clamp has to wrap the outer wall, which can be a quarter to two-thirds of an inch bigger. Thick exhaust and sanitation hose show the widest gap between the two numbers.
What raw water hose clamp size fits a 1 inch intake?
A 1 in ID wire-reinforced intake hose is usually about 1.5 to 1.6 in OD. An SAE 24 (1.06 to 2.00 in) puts that near mid-range. An SAE 20 works but finishes about three-quarters closed, leaving little margin on a tight seacock tail. Confirm with a paper strip at the tailpiece.
Which marine hoses need two clamps?
ABYC guidance calls for two clamps at each end of every wet exhaust connection and at each fuel fill connection, and Practical Sailor’s summary adds hose on smooth sanitation spigots. Below-waterline raw water hoses are often doubled as good practice, but one correctly sized clamp is acceptable where the tail is too short for two.
What sanitation hose clamp size fits 1-1/2 inch toilet hose?
Rubber 1-1/2 in ID sanitation hose is commonly listed near 2.0 in OD, which sits in the middle of an SAE 32. Rigid-helix PVC sanitation hose can measure differently. Push the hose fully onto the fitting first: a stiff hose that stops short reads small and leaves no room for the second clamp.
Can I use a bigger clamp and just tighten it more?
Within limits. Near its minimum, the screw has little thread left for re-tightening once the hose takes a set, and you get a long band tail that snags. On double-clamped joints an oversize clamp may not close at the narrower outer position. Pick the size that puts your reading mid-range.
How do I convert marine clamp sizes from inches to mm?
Multiply inches by 25.4, so an SAE 32 at 1.56 to 2.50 in becomes about 40 to 64 mm. If you measured circumference in millimeters, divide by 3.1416 for the OD and compare it with the mm column. Metric-coded clamps, such as 40–60 mm, are labelled in millimeters and don’t use SAE numbers.
Turning your walk-around notes into an order: send OneTouch Exim your list joint by joint, with the system, printed hose ID, installed OD from your strip or calipers, clamps per joint, and any part numbers stamped on the old clamps. Say whether each joint sees seawater full time, coolant heat or just spray, and whether you need 316. We’ll match sizes against our marine hose clamp size chart and tell you plainly which items we can supply. Use the clamp quote request form or WhatsApp +91-7838759114.