An exhaust clamp size chart works from the pipe, not the hose: you measure the outside diameter (OD) of the exhaust tube, and that number is the clamp size for U-bolt, lap-joint and butt-joint band clamps. A 2-1/2 in (63.5 mm) OD tube takes a clamp labelled 2-1/2 in, even where the clamp sits over the expanded end. V-band clamps are the exception, because they are sized to the flange.
Most wrong orders start with the wrong number: the inside diameter, the swaged socket, a metric tube half a millimetre off the inch size, or a V-band stamp. This exhaust clamp size chart sorts those out, covers 1-1/2 in car tubing to 8 in truck stacks, and shows how to measure pipe that is rusty or no longer round. For hose clamp sizing in general, use our hose clamp size chart in mm and inches; this page covers exhaust joints only.
One note on supply before the chart. OneTouch Exim stocks V-band clamps for turbo, EGR and DPF joints, but U-bolt muffler clamps and lap-joint or butt-joint exhaust bands are not part of our range. The U-bolt and band rows below are here so you can size correctly whoever you buy from.
Exhaust clamp size chart: the quick answer
- U-bolt muffler clamp: order the nominal tube OD of the joint (2 in tube, 2 in clamp). The saddle fits over the expanded end because the clamp is made slightly larger than the tube.
- Lap-joint band clamp: order the OD of the tube that slides in, the unexpanded pipe. The band is formed to sit on the larger, expanded socket, but the label carries the tube size.
- Butt-joint band clamp: order the OD shared by both pipes, which must be equal.
- V-band clamp: order by the clamp’s nominal diameter and profile, matched to the flange or to the old clamp’s part number. Tube OD alone is not enough.
- Never order an exhaust clamp by the pipe’s inside diameter.
Four diameters on an exhaust joint, and when each one matters
A slip joint has three measurable diameters and a flanged joint adds a fourth. Mixing them up is the biggest cause of returned exhaust clamps.
Tube OD: the number the chart uses
Exhaust tubing is named by its outside diameter. A “3 inch exhaust” is 3.00 in (76.2 mm) across the outside, whatever the wall thickness. Clamp makers follow the same convention: Donaldson’s heavy-duty accessory catalogue heads its clamp tables “O.D. Pipe” and lists 2.00 in (51 mm) through 6.00 in (152 mm) (Donaldson exhaust accessories catalogue). Tube OD is the number to measure, write down and quote.
Tube ID: useful for flow, useless for clamps
The inside diameter is the OD minus twice the wall. On 16-gauge tube (about 0.065 in, 1.65 mm wall) a 2-1/2 in tube has an ID of roughly 2.37 in. ID governs flow, and some tailpipe tips are listed by it, but a clamp never touches the bore, so an ID reading will push you one size too small. If the only number you have is an ID, add twice the wall thickness before you look anything up.
Expanded (swaged) socket OD: what the clamp actually sits on
On a slip joint, one pipe end is opened up so the next pipe can slide inside. The socket’s inside diameter is about the tube OD plus a small clearance, so its outside is larger again by two wall thicknesses. As an illustrative example, a 2.50 in tube with a 0.065 in wall, swaged to accept another 2.50 in tube with a little clearance, ends up with a socket OD of roughly 2.64 to 2.66 in. That is the surface a U-bolt saddle or lap-joint band actually bears on.
Torca’s lap-joint patent describes the same layout: the outer pipe end is diametrically enlarged, the inner pipe slides in, and the band wraps the enlarged sealing zone and collapses it onto the inner pipe (US 7,246,826). The socket OD matters when you check whether a clamp will physically pass over the joint and when a pipe is borderline between two sizes. It is not the label you order by.
Flange OD: only for V-band joints
A V-band joint has two machined or formed flanges welded to the pipe ends. The clamp grips the flange profile, so its size depends on the flange’s outer diameter and wedge shape, not on the pipe running into it. A 3 in turbo downpipe can carry a flange that needs a clamp labelled 3.50 in or more, so V-band rows sit in their own section below.
Exhaust clamp sizes by tube OD: the main chart
This exhaust clamp size chart lists common tube ODs in inches and millimetres, the nearest metric tube, and the clamp label to order in each style. Availability notes come from the maker ranges cited below; check your supplier’s list for odd sizes.
| Tube OD (in) | Tube OD (mm) | Nearby metric tube | U-bolt clamp: order | Lap-joint band: order | Butt-joint band: order |
|---|---|---|---|---|---|
| 1-1/2 | 38.1 | 38 mm | 1-1/2 in (standard 5/16 in U-bolt) | Rarely catalogued; use narrow seal clamp or U-bolt | Rarely catalogued |
| 1-5/8 | 41.3 | 41 to 42 mm | 1-5/8 in | Rarely catalogued | Rarely catalogued |
| 1-3/4 | 44.5 | 45 mm | 1-3/4 in | 1-3/4 in seal clamp (AccuSeal range starts here) | Limited |
| 1-7/8 | 47.6 | 48 mm | 1-7/8 in | Limited | Limited |
| 2 | 50.8 | 50 or 51 mm | 2 in | 2 in | 2 in |
| 2-1/4 | 57.2 | 57 mm | 2-1/4 in | 2-1/4 in | 2-1/4 in |
| 2-3/8 | 60.3 | 60 mm | 2-3/8 in | Often not stocked; check list | Check list |
| 2-1/2 | 63.5 | 63 or 63.5 mm | 2-1/2 in | 2-1/2 in | 2-1/2 in |
| 2-3/4 | 69.9 | 70 mm | 2-3/4 in (heavy 3/8 in U-bolt) | 2-3/4 in | 2-3/4 in |
| 3 | 76.2 | 76 mm | 3 in | 3 in | 3 in |
| 3-1/2 | 88.9 | 89 or 90 mm | 3-1/2 in | 3-1/2 in | 3-1/2 in |
| 4 | 101.6 | 101.6 or 102 mm | 4 in (extra heavy duty) | 4 in | 4 in |
| 4-1/2 | 114.3 | 114 mm | 4-1/2 in | 4-1/2 in | 4-1/2 in |
| 5 | 127.0 | 127 mm | 5 in (truck or guillotine style) | 5 in | 5 in |
| 6 | 152.4 | 152 mm | 6 in (guillotine style) | 6 in | 6 in |
| 7 | 177.8 | 178 mm | Uncommon | 7 in seal clamp (AccuSeal range ends here) | Flat-band style; check list |
| 8 | 203.2 | 203 mm | Uncommon | Special order | Flat-band style (some ranges reach 10 in) |
How makers label U-bolt, lap-joint and butt-joint clamps
U-bolt clamps carry the nominal pipe size, and the AP Exhaust clamping catalogue splits them by duty: standard 5/16 in U-bolts from 1-1/8 in to 2-1/2 in, slotted heavy-duty 3/8 in U-bolts from 1-1/2 in to 3 in, extra-heavy-duty 3/8 in with an 11-gauge saddle from 2 in to 6 in, plus truck and guillotine clamps from 2-3/4 in upward (AP Exhaust clamping products catalogue). The clamp is meant to slip over the joint, which is why it ends up a touch larger than the tube. An older muffler-clamp patent states plainly that U-bolt clamps are larger in diameter than the tubing they go on (US 4,249,759). Some counters also sell in-between labels such as 2-1/8 in; those suit a thick-walled socket or an imperial tube with a slightly oversize swage.
Lap-joint band clamps cause the most confusion. The band seats on the expanded socket, so in a physical sense it is sized to the larger pipe. Yet the label you buy by is the tube size of the joint, which equals the OD of the inner, unexpanded pipe. Walker’s lap-joint listings give a single “pipe diameter” (2.5 in, 5 in and so on) and describe the clamp as joining an ID to an OD, and other distributors list pre-formed lap clamps by “tube O.D.” A 2-1/2 in lap clamp therefore fits a joint where a 2-1/2 in tube slides into a socket swaged from 2-1/2 in tube. The step or forming inside the band takes care of the extra socket diameter. AP lists lap-joint band clamps from 2 in to 6 in, so below 2 in you will usually be choosing a seal clamp or a U-bolt.
Narrow seal clamps for slotted overlap joints follow the same convention. NORMA’s Torca AccuSeal is offered from 42 mm (1-3/4 in) to 177.8 mm (7 in) in standard industry sizes (NORMA Torca AccuSeal), and NORMA’s own shop lists a 2.00 in seal clamp as 50.8 mm, which is the tube OD in millimetres.
Butt-joint band clamps join two pipes of the same OD end to end, so there is only one diameter to match. AP lists them from 2 in to 6 in in quarter-inch steps. If the two pipe ends measure differently, a butt clamp is the wrong part, however close the numbers look. Which of the two band styles, or a U-bolt, suits your joint is a separate question covered in band clamp vs U-bolt clamp.
Heavy truck exhaust sizes, 5 to 8 inches
Class 6 to 8 trucks, buses and off-highway machines mostly run 4 to 6 in tube, with some stacks at 7 or 8 in. Three things change. First, published ranges thin out: many lap and butt ranges stop at 6 in, seal clamps reach 7 in, and flat-band clamps are offered up to 10 in by some makers. Second, the tube is often heavier wall, so the socket OD sits further above the nominal size; measure it before assuming a light-duty clamp will pass over. Third, many truck joints in that range are V-band or flat-band at the DPF and SCR cans, so check whether the joint is flanged before ordering a band. Donaldson, for instance, sizes its seal and U-bolt clamps by pipe OD up to 6.00 in (152 mm) but its V-bands by part diameter.
Metric vs imperial exhaust tube: the half-millimetre trap
North American exhaust tube is made to inch ODs; European and Asian vehicles mostly use round millimetre sizes. Labels often say “2.5 in / 63 mm” as if they were the same. They are not, and on a slip joint the difference shows.
| Inch tube | Exact mm | Common metric tube | Difference | What happens if mixed |
|---|---|---|---|---|
| 1-3/4 in | 44.45 | 45 mm | 0.55 mm | 45 mm pipe may not enter a tight 1-3/4 in swage |
| 2 in | 50.80 | 50 mm or 51 mm | 0.80 mm under / 0.20 mm over | 50 mm pipe is loose in a 2 in socket; 51 mm is close to a match |
| 2-1/4 in | 57.15 | 57 mm | 0.15 mm | Usually interchangeable |
| 2-1/2 in | 63.50 | 63 mm | 0.50 mm | Extra slip clearance; more band take-up needed to seal |
| 3 in | 76.20 | 76 mm | 0.20 mm | Usually interchangeable |
| 3-1/2 in | 88.90 | 89 mm or 90 mm | 0.10 mm / 1.10 mm | 90 mm pipe may not fit a 3-1/2 in socket |
| 4 in | 101.60 | 100 mm or 102 mm | 1.60 mm / 0.40 mm | 100 mm pipe is clearly loose in a 4 in socket |
Why half a millimetre matters: a band clamp seals a lap joint by pulling the slotted socket down onto the inner pipe. Every bit of extra clearance between socket and pipe uses up band travel before any sealing pressure builds. A 63 mm pipe in a socket swaged for 63.5 mm tube adds about 1.6 mm of circumference to close. A good band copes with that, but a clamp already near the end of its travel on a heavy-wall socket may bottom out and leak. A U-bolt will close the gap by crushing, which is one reason U-bolts “work” on mismatched joints and then leave a pipe that cannot be separated cleanly.
The reverse case is worse. A 51 mm or 90 mm pipe may not enter an inch-size socket at all without re-expanding it. When you are fitting European parts into a US system, or the other way round, measure both pipe ends before ordering anything, and write the clamp size in the unit of the pipe the clamp will sit on.
How to measure exhaust pipe diameter on a real vehicle
Our general guide on how to measure hose clamp size covers calipers, pi tapes and the common reading errors. What follows is only what is different about exhaust pipe: heat, scale, ovality, swaged ends and old hardware.
Calipers on a clean, straight section
- Let the system cool. A pipe that has just been running can burn you through gloves, and hot steel reads slightly large.
- Pick a straight run at least two diameters away from bends, hangers and welds. Bends are rarely round.
- Scrape or wire-brush a narrow ring to bare metal. Scale and flaking aluminised coating can add 0.5 mm or more to a reading.
- Take two readings at right angles. If they differ by more than about 1 percent of the diameter, treat the pipe as oval and use a tape (below).
- Match the average to the nearest size in the chart. A 63.4 mm average on a US vehicle is 2-1/2 in tube; on a European car it may be 63 mm tube.
Circumference tape on hot, rusty or out-of-round pipe
Exhaust pipe goes oval with age from hanger loads, old U-bolt crushes or a misplaced jack, and calipers then read whichever axis you catch. A flexible tape or a strip of paper wrapped once around the pipe gives the perimeter instead, and the perimeter is what a band clamp works on, because a band wraps the whole circumference. Divide the circumference by pi (3.1416) to get an equivalent round OD.
- A wrap of 7.85 in gives 7.85 / 3.1416 = 2.50 in OD.
- A wrap of 239.4 mm gives 76.2 mm, which is 3 in tube.
- Pull the tape snug and level, not spiralled; a slanted wrap reads long.
- On heavily scaled pipe, measure on bare metal, or the scale layer adds about 3 mm of perimeter for each 0.5 mm of crust.
Measuring the swaged end of a slip joint
Measure the socket as well as the tube. You need both numbers for three reasons: to confirm the joint really is a slip joint (the socket should be larger than the tube by roughly two wall thicknesses plus clearance), to check the clamp will pass over it, and to spot a socket that has been crushed by an old U-bolt. Take the socket reading in the middle of the overlap, where the band or saddle will sit, not at the flared lip. If the socket is slotted, measure away from the slots or the reading will be low.
A quick sanity check is to subtract the tube OD from the socket OD. On light-vehicle tube, a difference of roughly 3 to 4 mm (about 1/8 in) is typical of a fresh swage on 16-gauge tube (illustrative). Much less than that and the socket has probably been crushed or the “socket” is really a separate pipe of the same size, which needs a butt clamp. Much more and the joint may be a reducer, which needs a reducing clamp or a sleeve.
Reading an old U-bolt saddle
An old clamp can tell you the size. A stamped or tagged size on the saddle is the most reliable source. Without a stamp, measure the inside of the saddle curve across its tips, and the distance between the inside faces of the U-bolt legs. Both should be a little larger than the tube OD. Do not measure the crushed pipe under the saddle: by design that area has been deformed and will read small in one direction and large in the other. Also check the rod: a 5/16 in rod points to the standard-duty range and a 3/8 in rod to heavy duty, which matters if you are replacing like for like on a truck.
V-band flanges: measure the flange, not the pipe
On a V-band joint, record the flange OD and profile, and the clamp’s band width and part number if one is fitted. The full flange method (outer diameter, wedge angle, flange thickness, male and female pairs) is in our V-band clamp selection guide, so we will not repeat it here. The key point for this chart is that a V-band size number is never a pipe OD.
V-band clamp sizes OneTouch stocks
OneTouch Exim lists 87 V-band clamp sizes across general exhaust and turbo, EGR and DPF use. Each product page gives a nominal diameter in inches and millimetres, the band width, the insert profile dimensions (thickness, apex width and depth), and the OEM and aftermarket part numbers it replaces. Our pages do not state what physical point the nominal diameter is measured to, so match by part number or by comparing the profile dimensions with your old clamp. A selection:
| OneTouch part | Nominal size | Category | Band width | Example OEM reference on page |
|---|---|---|---|---|
| 4VC0288 | 2.88 in (73.2 mm) | Exhaust and turbo, general purpose | 0.75 in | Detroit Diesel 8920206 |
| 4VC0321A | 3.21 in (81.5 mm) | Turbo | 0.75 in | Mack / Volvo 20592787 |
| 4VC0321MK | 3.21 in (81.5 mm) | EGR | 0.625 in | Mack / Volvo 21167013 |
| 4VC0350 | 3.50 in (88.9 mm) | Turbo | 0.875 in | Caterpillar 8N0878 |
| 4VC0481 | 4.81 in (122.2 mm) | DPF and aftertreatment | 0.875 in | Volvo 21021852 |
| 4VC0532 | 5.32 in (135.1 mm) | Exhaust and turbo, general purpose | 0.775 in | Cummins 52121285AA |
| 4VC0649 | 6.49 in (164.8 mm) | Exhaust and turbo, general purpose | 0.875 in | Cummins 2880213 |
| 4VC1050 | 10.50 in (266.7 mm) | DPF and aftertreatment | 0.875 in | Detroit Diesel A6809950202 |
Notice that the two 3.21 in clamps share a nominal diameter but differ in band width and application. That is why a size number alone is not an order for a V-band. If you only have a pipe OD and no part number, send us the flange measurements and photos and we will match it from the cross-reference data. The listings give no stainless grade, so raise it in your enquiry if it matters; our 304 vs 316 exhaust clamp article covers the material side.
Between sizes and out of round: fixes that work
Real pipes do not always land on a chart row. Use your exhaust clamp size chart reading with this table for in-between cases.
| What you measured | Likely cause | Practical fix |
|---|---|---|
| Tube reads between two inch sizes (e.g. 2.38 in) | 2-3/8 in or a 60 mm metric tube | Check for a 2-3/8 in or 60 mm clamp before rounding; a U-bolt is the most likely to exist in that size |
| Two caliper readings differ by more than 1 percent | Oval pipe from an old U-bolt, a hanger or a jack | Re-round with a pipe expander or sizing tool, then size from the tape circumference |
| Socket OD barely bigger than tube OD | Socket crushed by a previous U-bolt | Re-expand the socket or replace the pipe section; a band clamp will not seal a crimped joint well |
| Metric pipe into inch socket (or reverse) | Mixed-origin parts | Measure both ends; if clearance exceeds about 1 mm on diameter, re-swage or use a reducing sleeve |
| Two pipe ends of different OD, no swage | Reducer joint | Use a reducer fitting plus the correct clamp, not an oversize butt clamp |
| Socket heavier wall than the clamp expects | Truck tube, 14-gauge or thicker | Choose a heavy-duty or thick-wall clamp design and confirm the socket OD against the clamp’s opening |
Do not size up to cover ovality. A band one size larger than the tube will reach full travel before it pulls the joint tight, and a U-bolt one size up crushes harder and leaves a deeper crease. The better order of work is: restore the pipe to round, then fit the clamp the chart calls for. A tailpipe expander or pipe sizing tool will do this on most light-vehicle tube; heavy truck tube usually needs the section replaced.
Do not size down to “get more bite”. A smaller U-bolt may not fit over the socket at all, and a smaller band simply will not wrap. NORMA’s DuraSeal is an example of a design made for thicker walls and larger assembly gaps, offered from 50 mm (2 in) to 89 mm (3-1/2 in); clamps like that solve a tolerance problem in a way an undersized standard clamp cannot.
Watch the overlap length. A lap-joint band needs enough overlap under it to seal, and the band should cover the slot ends in a slotted socket. If you have trimmed a pipe to fit, measure the overlap before ordering a wide band. When the overlap is short, a narrow seal clamp or a U-bolt may be the only part that fits; choosing between them is covered in how to choose an exhaust clamp, and the basic types are explained in what is an exhaust clamp.
Exhaust clamp sizing questions buyers ask
Is exhaust clamp size the pipe OD or ID?
The OD. U-bolt, lap-joint and butt-joint clamps are labelled by the outside diameter of the exhaust tube. Ordering by the inside diameter will usually put you one size too small.
Should a lap-joint clamp be sized to the expanded pipe or the inner pipe?
The band physically sits on the expanded socket, but the label is the tube size of the joint, which is the OD of the inner pipe. A 2-1/2 in lap clamp is for a 2-1/2 in tube sliding into a 2-1/2 in swaged socket. Measure the socket too, to confirm the clamp will pass over it.
What size U-bolt clamp do I need for a 2-1/2 inch exhaust?
A clamp labelled 2-1/2 in. U-bolt clamps are made slightly larger than the tube so the saddle fits over the swaged end. If the socket is unusually thick, some counters stock an in-between size such as 2-5/8 in; check the saddle against your measured socket OD.
How do I measure an exhaust pipe that is oval?
Wrap a flexible tape once around the pipe on bare metal and divide the circumference by 3.1416. That gives the round-equivalent OD. If the pipe is badly oval, re-round it before fitting a band clamp.
Is a 3.50 in V-band clamp for a 3.5 inch pipe?
Not necessarily. The V-band number relates to the flange and clamp, not the pipe bore, and the flange is usually larger than the tube. Match a V-band by its part number or by flange OD and profile.
Does OneTouch sell U-bolt or band exhaust clamps?
No. Our exhaust-side range is V-band clamps (turbo, EGR, DPF); hose joints are served by our T-bolt and worm gear lines. For U-bolt and lap or butt band clamps, use this chart to size the part with your exhaust supplier.
Send the pipe numbers, get the right V-band
If your joint is flanged, look up the old clamp’s number in our clamp cross-reference index; most OEM and aftermarket V-band numbers map straight to a OneTouch part. No number on the old clamp? Write down the tube OD, the flange OD and the band width, add a photo of the profile, and send them to our team for a matched quote.