German Type Hose Clamp Size Chart and How to Measure Correctly

A German type hose clamp size chart lists each clamp by its clamping range in millimetres and its band width, for example 20-32 mm on a 9 mm band. To pick a size, measure the outside diameter of the hose as it sits on the fitting, then choose the range that puts that number in its upper-middle part.

Below, the sizes are laid out as a ladder, one rung per size, showing how far each range reaches and how much it shares with the next. Then come measuring steps for soft and thin-wall hose, four worked examples, the band marking, and the closest clamps OneTouch Exim supplies (we do not stock the German design itself).

If you want the background first, our explainer on what a German type hose clamp is covers the solid band and pressed thread, and the DIN 3017 standard explained post covers the standard behind the sizes, including a plain metric-to-inch conversion. This page does not repeat either. It is about reading the ladder and landing on the right rung.

How the German type hose clamp size chart is built

German type sizes are not numbered the way SAE clamps are. There is no “size 16” or “size 24”. Each clamp is named by the smallest and largest diameter it can close on, in millimetres, plus the band width. So a clamp sold as 25-40/9 grips anything from 25 mm to 40 mm across, on a 9 mm wide band. That naming makes the chart self-explanatory once you know two things: where each range starts and stops, and how much each range overlaps the next.

We built the two ladders below from published maker data rather than from one maker’s table. The main source is the NORMA TORRO data sheet, which lists clamping ranges to DIN 3017-1 for 9 mm and 12 mm bands. We cross-checked the small and mid sizes against the Mikalor ASFA-L listing at Bossard, the DIN 3017 W2 range at Kloska and a Würth DIN 3017 shape A clamp. Where makers disagree on a rung, the table says so. The inch, span and overlap columns are our own arithmetic.

Columns in each ladder

• Range (mm): the clamping range as it is stamped on the band and printed on the box.
• Range (in): the same limits divided by 25.4 and rounded to two decimals. Use it to compare with an SAE clamp, not to order a German one.
• Span (mm): the largest minus the smallest diameter. It tells you how forgiving the size is if your measurement is a little off.
• Overlap with next size (mm): how many millimetres this rung shares with the rung above it. Inside that overlap zone, both sizes fit.

9 mm band hose clamp sizes: the light-series ladder

The 9 mm band is the everyday width for hoses up to about 50 to 60 mm. It is the one most workshop assortment boxes are filled with, and the one you will find on most small coolant, fuel-return, vacuum, washer and water lines on European-built equipment. Below 16 mm some makers drop to a narrower 7 or 7.5 mm band, so check the band width before you assume 9 mm on the smallest sizes.

Two things stand out. The bottom of the ladder is tight: the smallest rungs cover only 4 to 6 mm, so a 2 mm measuring error can put you on the wrong size. And from 40-60 upward every rung is a 20 mm window starting 10 mm above the last.

Watch for the rungs where makers differ. One catalogue sells 16-25 while another sells 16-27; one sells 32-50 while NORMA prints 35-50 and notes 32-50 in brackets for some materials. If your measured diameter sits right on one of those disputed edges (25 to 27 mm, or 32 to 35 mm), choose the neighbouring rung instead so the brand you are sent does not matter.

12 mm band hose clamp sizes: the heavier ladder

The 12 mm band carries the same range names from about 16 mm upward and keeps going far beyond where the 9 mm band normally stops. It is the usual choice on large coolant hoses, air intake couplers, ducting and industrial suction hose. Some distributors also sell a 12-20 rung on 12 mm band, while NORMA’s sheet starts the 12 mm ladder at 16-27.

Where both widths exist for the same range, the range name is identical: a 40-60/9 and a 40-60/12 close on exactly the same diameters. Band width changes how the load is spread over the hose and how much torque the clamp tolerates, not which hose it fits. Our guide on how to choose a German type hose clamp deals with the width decision, so here we only use width as the second half of the size name.

Reading the ladder: overlap zones and choosing between two sizes

Every rung shares part of its range with the rung above. On the large sizes that shared zone is 10 mm wide, so half of every 20 mm window is also covered by the next size. That is deliberate. It means a hose that measures 65 mm can be clamped with either 50-70 or 60-80, and a buyer is never stranded between two sizes. It also means the chart alone does not tell you which of the two to buy. You need a rule.

Aim for the upper-middle of the range

Work out where your measured diameter sits inside each candidate range, as a fraction of the span from the small end. 65 mm sits 75% of the way up a 50-70 clamp and 25% up a 60-80. Prefer the size where your figure falls between about 50% and 80%: here, 50-70.

The reason is the direction of travel. A worm drive clamp only ever gets smaller as you tighten it. The diameter you measure before fitting is the starting point, and the hose then compresses under the band, often by a millimetre or two on firm rubber and more on silicone. If you start in the upper-middle, the clamp finishes near the middle of its range, with plenty of screw thread still engaged and room to re-tighten after the hose takes a set. If you start in the bottom quarter, the clamp is already close to its minimum before you begin, the spare band tail is long, and there may be little travel left when the hose settles.

Why not the very top of the range

At the top end only a short length of the pressed thread is engaged, so the load runs through fewer ridges and the screw can be awkward to start. The clamp also has to open over a bead, flare or barb on the way to its seat. Stay below about 85% of the span unless there is no alternative.

Why German ranges are narrower than SAE ranges

A German 20-32 clamp spans 12 mm. An SAE 16 clamp spans roughly 21 to 38 mm, about 17 mm, and the SAE sizes above it span more than 20 mm. German ranges suit assembly lines that stock one clamp per known joint, and a short span keeps the closed shape and housing position consistent, which helps the solid band close evenly on soft hose. SAE ranges suit an aftermarket that wants as few part numbers as possible. So expect more rungs on a German chart than on an SAE chart for the same diameter range, and expect to measure a little more carefully. The German type vs American type comparison covers the other design differences.

How to measure for a German type hose clamp

The general method (calipers versus pi tape, common reading errors, measuring each clamp family) is in our guide on how to measure hose clamp size. The steps below are the extra care that German type sizing needs, because the hoses that call for this clamp are often soft, thin or lined, and because the narrow rungs leave less room for error.

Measure the installed outside diameter, over the spigot

The figure that matters is the outside diameter of the hose where the band will sit, with the hose already pushed onto its pipe, barb or spigot. A hose stretched over a fitting is larger than the same hose lying loose on the bench, sometimes by several millimetres. If the hose is not yet fitted, add the fitting’s outside diameter to twice the hose wall thickness. Never size from the hose bore or the nominal hose size printed on the hose; a “25 mm” hose is 25 mm inside, and its outside could be 31 mm or 35 mm depending on the wall.

Soft silicone and thin-wall hose: tape, not calipers

Caliper jaws squeeze silicone. Close them with normal finger pressure on a silicone coupler and the reading can come out a millimetre or more small, and on a 4 mm German rung that is enough to choose the wrong size. For silicone, thin-wall PVC and soft rubber, wrap a pi tape (or a strip of paper you mark and then lay against a rule) around the hose at the clamp seat. Divide a paper circumference by 3.1416 to get the diameter. If calipers are all you have, touch the jaws to the hose without squeezing, take readings at two angles 90 degrees apart, and use the larger one, since hose on a spigot is rarely perfectly round.

Firm rubber and reinforced hose: calipers are fine

On firm EPDM coolant hose, fuel hose and wire-reinforced suction hose, calipers give a quick, repeatable reading. Take it where the band will sit, which is usually a few millimetres behind the bead or the last barb ridge, not over the ridge itself. Then check separately that the top of the range is bigger than the ridge, because the clamp has to pass over it on the way on.

Adding liner or sleeve thickness

If anything goes between the hose and the band (a separate protective liner, a heat sleeve, a rubber strip on a ducting joint, or a second hose slid over the first), measure over it or add its thickness twice. A 1.5 mm sleeve adds 3 mm to the diameter. That is half the span of a 10-16 clamp. Fitted liners built into a clamp are different: their thickness is already accounted for in the clamp’s stated range, so you measure the bare hose as usual.

Record two numbers, not one

1. Seated diameter: the hose outside diameter at the clamp position, fitted.
2. Pass-over diameter: the largest diameter the open clamp must slide over (bead, flare, barb ridge, or a hose end that has swollen with age).
3. Choose the rung where the seated diameter falls in the upper-middle and the pass-over diameter is still inside the range.
4. Note the band width on the original clamp or drawing, then write the size as range/width, for example 40-60/12.

Four worked sizing examples

Hose wall thicknesses below are illustrative values for common hose types, chosen to show the method. Use your own measurement on the real part.

Example 1: 57 mm silicone coupler on an intercooler pipe

A straight silicone coupler with a 57 mm bore (sold as 2-1/4 in) joins two 57 mm aluminium pipes. The wall is about 4.5 mm (illustrative), so the installed diameter is roughly 57 + 4.5 + 4.5 = 66 mm. A pi tape over the fitted coupler reads 66.3 mm. Candidates are 50-70 (66 sits at 80% of the span) and 60-80 (30%). Choose 50-70, because silicone will compress noticeably and a clamp starting at 30% could run short of travel. Pick the 12 mm band, which spreads the load better on soft hose: 50-70/12.

Example 2: 3/4 in heater hose on a brass spigot

An EPDM heater hose with a 19 mm (3/4 in) bore and a wall of about 4 mm (illustrative) goes onto a spigot slightly larger than its bore. Calipers at the clamp seat read 28 mm. Candidates are 20-32 (28 sits at 67%) and 25-40 (20%). The 16-27 rung is too small. Choose 20-32/9. The next size up would leave a long tail lying against nearby hoses.

Example 3: 25 mm garden or irrigation hose on a barbed fitting

A reinforced PVC hose with a 25 mm (1 in) bore is pushed over a barbed tail. Behind the last barb, calipers read 33 mm; over the barb ridge itself the hose measures 36 mm. Candidates are 25-40 (33 at 53%) and 30-45 (20%). 25-40 fits both numbers: the seated 33 mm is in the upper-middle and the 36 mm ridge is well inside the top of the range. Choose 25-40/9. If you had sized from the bore, you would have picked a 16-27 clamp that cannot even reach the hose.

Example 4: 102 mm (4 in) air intake hose

A 4 in intake elbow with a 102 mm bore and a wall of about 5 mm (illustrative) fits over a 102 mm pipe. The pi tape reads 112 mm. Candidates are 100-120 (60%) and 110-130 (10%). Choose 100-120/12. On a large intake the 9 mm band is available in the same range, but the wider band gives a more even seal on a big, flexible diameter, and engine vibration makes the extra contact area worth having. If the joint carries charge-air pressure rather than plain intake suction, a worm drive clamp may not be the right family at all; see the alternatives section below.

Decoding the marking on a German hose clip band

When you are replacing a clamp, the old one often tells you the size directly. NORMA’s data sheet notes that material and clamping range are stamped on the band, and most reputable German type makers do the same. A typical stamp reads something like W4 16-25/9, sometimes with the maker’s logo and “DIN 3017” beside it. Read it in three parts:

• W4: the material class. In NORMA’s scheme W1 is zinc-plated steel throughout, W2 is a 430 ferritic stainless band and housing with a plated steel screw, W4 is 304 stainless throughout and W5 is 316 stainless throughout. Our post on W1, W2, W4 and W5 hose clamp classes explains each in full.
• 16-25: the clamping range in millimetres, smallest to largest. This is the rung on the ladder.
• /9: the band width in millimetres. A /12 means the 12 mm band.

Distributor codes may reorder the parts (for example “16-25/9W2”), but the content is the same: range, width, material. Maker article numbers do not decode into a size, so look those up in the maker’s catalogue. If the stamp has worn off, measure the hose, not the old clamp, which has been pulled smaller than its rated range.

For grade choice beyond what the W class tells you, our 304 vs 316 German type hose clamp guide covers when W5 is worth the extra cost.

Common mistakes when reading a metric hose clamp size chart

• Taking the first range that contains the number. Because ranges overlap, the first match is often the size where you sit in the bottom quarter. Check the next rung down as well.
• Ignoring band width on the order. “40-60” alone can arrive as a 9 mm or a 12 mm band. Write both.
• Converting the range to an SAE number by arithmetic alone. Choosing the SAE size that puts your diameter mid-range is a separate step from converting units. See the cross-reference table below and our hose clamp size chart in mm and inches for the full SAE list.

OneTouch Exim and German type sizes: closest alternatives we supply

To be clear: OneTouch Exim does not stock German type (DIN 3017) clamps. Every worm drive clamp we sell is the American, SAE-numbered pattern: perforated band, inch hex screw. If a drawing or service manual specifies a DIN 3017 clamp or a W class, a German type clamp from a European maker is the correct part, and we would rather tell you that than sell a substitute that does not meet the drawing.

Many buyers, though, come to a German type size chart because they want the hose-friendly band on silicone or soft rubber, not because a drawing demands DIN 3017. For them, our lined clamp range is the closest match. Here a smooth liner sits under the slotted band, so soft hose has nothing to squeeze up into. Two lined builds and one unlined option are worth knowing:

• 4CL94xx, stainless steel all: per the product pages, the band and housing are 301 stainless, the screw is 410 stainless, the band is 1/2 in wide and the rating is 45 in-lb. Example: the 4CL9440 lined clamp, 2.06 to 3.00 in (52 to 76 mm).
• 4CL00xx: lined the same way but fitted with a zinc-plated carbon steel screw, for dry interior use where cost matters more than screw corrosion.
• 4SS all-stainless, unlined: for firm hose where the slots are not a problem, such as reinforced garden hose or EPDM. Example: the 4SS0016, 0.81 to 1.50 in (21 to 38 mm), built from 301 (band, housing) and 410 (screw). It is not 316.

German range to OneTouch lined clamp: cross-reference

The table maps common German rungs to the 4CL94xx size that puts the same diameter in a sensible part of its range. Because SAE ranges are wider and start at different points, this is a match by diameter, not a one-to-one part interchange. Always check your measured diameter against the SAE range before ordering.

Applying this to the worked examples: the 28 mm heater hose suits the 4CL9412 (17 to 32 mm), where it sits at about 73% of the range. The 66 mm silicone coupler suits the 4CL9440, at about 58%. The 112 mm intake suits the 4CL9472 (105 to 127 mm), at about 32%. That is lower than we would choose on a German ladder, but the next size down tops out at 114 mm, too close to the reading. The 33 mm garden hose is firm PVC, so an unlined 4SS0016 does the job.

Some lined clamp pages also list NORMA part numbers in their cross-reference tables, which helps if your parts book already uses those numbers. If you have a list of German clamp numbers or DIN ranges, our clamp cross-reference index covers several thousand OEM and aftermarket numbers, and we can flag lines that need a true DIN 3017 part instead of an SAE alternative. For a boosted intake joint like Example 4, ask us about a T-bolt or constant torque clamp rather than any worm drive design.

German type hose clamp sizing questions buyers ask

Send us your measured diameters

If you have a list of German ranges, old band markings or simply measured hose diameters, check them against our cross-reference first. For anything it does not settle, send the list through our contact page with the hose type next to each diameter. We will reply with the lined or all-stainless SAE size for each line, and tell you plainly which ones need a true DIN 3017 clamp from another source.