No equivalent standard is recorded for a DIN 3570 U-bolt, and no published cross-reference converts a DIN 3570 size into another standard’s size. The ASME, MSS and national documents that cover similar parts sit outside the DIN framework: each has its own size system and its own designations, and none is recorded as corresponding to DIN 3570. What is available to a buyer is therefore not an equivalent but an alternative — a U-bolt or bent bolt built to another standard that performs the same function. An alternative is usable only once you have proved, dimension by dimension, that it fits the pipe, the support and the fastening. That is a dimensional review, not a cross-reference.
The standard itself is still current: DIN 3570, dated October 1968, is listed as in force and carries no successor designation, so a drawing that cites it is citing a live document rather than a withdrawn one. That is exactly why the substitution question is harder than it looks. There is no newer document to move to and no published equivalence to lean on. Everything rests on the dimensions.
Why “equivalent” is the wrong word until it has been checked
The word gets used for three different things in fastener trade, and only one of them allows a part to be swapped without further work.
- Identical — the two documents specify the same dimensions and the same requirements. Nothing about DIN 3570 is in this category.
- Interchangeable — the documents differ, but at the size you need every dimension that matters agrees, so the part drops into the existing assembly. This is a conclusion you reach size by size, after checking. It is not a property of a standard number.
- Functionally similar — both parts are round-bar U-bolts that clamp a pipe to a support. This is true of most of the documents below, and it is not enough to authorize a substitution on its own.
A supplier quoting “the equivalent” is usually describing the third case. Treat that as an invitation to check, not as a finding.
What DIN 3570 actually fixes
DIN 3570, titled Rundstahlbügel für Rohre — Steel strap for tubes of NW 20 to 500, is a dimensional standard for a round-bar U-bolt with threaded ends, supplied without nuts and without washers. It fixes the size ladder, the pipe outside diameter each size suits, the thread on the legs, the minimum thread length, the leg centre distance, the overall height and the form. It does not fix material, grade, mechanical properties, coating or working load. Any of those may be stated on your drawing, but they come from somewhere else.
Four properties of the document shape every substitution decision that follows:
- The size number is an inside width in millimetres — not a pipe size and not a thread size. A 46 is 46 mm across the inside of the U; whether the legs are M10 or M12 is a separate table entry.
- The standard’s table runs to 17 sizes, from 30 to 530. A German supplier dimension table states that DIN 3570 covers nominal widths 20 to 500 and that dimensions outside that original range are manufacturer or supplier-programme versions rather than standard sizes — which is why a size 23 and sizes above 530 appear in catalogues as offerings in the style of the standard.
- It defines two forms. Form A has two equal threaded legs. Form B has one long threaded leg and one shortened leg, for positions that can only be reached and tightened from one side. Form B takes half the number of nuts, and suppliers normally list it only for the smaller sizes.
- It is metric throughout. Metric pipe outside diameters and metric coarse threads — M10, M12, M16, M20 and M24 across the standard’s table.
The documents that get proposed as replacements, and what each one really covers
Several documents come up in this conversation, and they are not the same kind of document. One is a product standard for bent bolts, one is a pipe-support standard that selects and applies hangers, and one is a national designation for a related part. None is recorded as corresponding to DIN 3570.
| Document | What it is | Why it is not a DIN 3570 equivalent |
|---|---|---|
| DIN 3570 (1968-10) | German dimensional standard for round-bar U-bolts for pipes, nominal widths 20 to 500; sizes 30 to 530; forms A and B; metric threads | The reference document. Listed as in force, and no corresponding standard designation is recorded for it. |
| ASME B18.31.5 — Bent Bolts (Inch Series), 2011 (R2021) | ASME product standard for bent bolts. Dimensional tables for U-bolts of differing bends, eyebolts, hook bolts and J-bolts, plus general requirements for offset round bend, vee bend U-bolts and slant U-bolts. Two ordering systems, one of them a part identification number covering materials and finishes. Last reaffirmed in 2021 and now on stabilized maintenance. | It governs the same product family — bent bolts, U-bolts included. But it is an inch-series document, while DIN 3570 is metric in pipe outside diameter, bar diameter and thread. The two also organise a size differently: one indexes a bend to a pipe outside diameter in the metric series, the other to the inch-series configurations in its own tables. Nothing in either document maps a size across. |
| ANSI/MSS SP-58 — Pipe Hangers and Supports | Standard of the Manufacturers Standardization Society covering materials, design, manufacture, selection, application and installation of pipe hangers and supports. It uses its own type designations — Type 24 for the classic U-bolt — and is commonly applied alongside the ASME B31 piping codes, but it is not an ASME document. | It is a selection and application standard for the support system, not a bent-bolt product standard. A supplier technical page states plainly that DIN 3570 and MSS SP-58 are independent documents from different organisations, with their own type designations and measurement systems, that both describe the same part type functionally, and that direct dimensional interchangeability between them is not automatically given. |
| National designations, such as JIS B 2809 | JIS B 2809:2018 is a current Japanese standard whose recorded English title is U-bolt Wire Rope Grips, issued by the Japanese Standards Association. | A national designation describes the part that standard covers, in that standard’s size system. It is not convertible into a DIN 3570 size, and a size number from one carries no meaning in the other. |
The consequence is narrow and worth stating exactly: if a drawing calls up a DIN 3570 U-bolt, there is no standard you can name in its place. There is only a candidate part, which either matches on the dimensions below or does not.
The dimensions that decide whether a replacement fits
These are the data points to compare — 13 rows, three of which the standard does not cover at all. The middle column gives what DIN 3570 provides, using its own symbol where the standard has one. The right-hand column is what you have to find in the candidate’s document, or establish from its drawing, before the substitution can be called interchangeable.
| What to match | DIN 3570 symbol | What it decides |
|---|---|---|
| Pipe outside diameter range | d1 | Whether the U-bolt goes round the pipe. The standard gives a range for the smaller sizes — 38 to 42.4 mm at size 46 — because two metric OD series fit the same bolt. |
| Inside width of the U | size number a | Whether the pipe and any lining, sleeve or clamp shell seat inside the bend without being crushed or left loose. |
| Leg centre distance | e | Whether the legs enter the holes in the support, bracket or channel. 56 mm at size 46; 136 mm at size 120; 554 mm at size 530. |
| Bar / shank diameter | d2 | Strength and stiffness of the part, and the diameter that has to pass through the hole. Tabulated separately from the thread: about 8.9 mm at M10, 10.7 at M12, 14.6 at M16, 18.2 at M20 and 22 at M24. A rolled metric thread is formed on a bar slightly below the thread’s pitch diameter, which is why the bar is smaller than the thread. |
| Bend geometry | the drawing | Inside bend radius, whether the bend is round, square or vee, and where the bend sits relative to the pipe and the support. |
| Overall height | h1 | Clearance above the pipe, and whether the legs are long enough to reach the support at all. 86 mm at size 46; 171 mm at size 120; 589 mm at size 530. |
| Thread length | b, a minimum | Whether there is enough thread above the support to fit the nut and washer and still tighten. 50 mm at size 46; 60 mm at size 120; 70 mm at size 530. The minimum applies to each threaded leg: in Form A that means both legs, and in Form B it means the long threaded leg — the shortened leg carries no full thread length and is checked on its own dimensions instead. |
| Thread size and pitch | d3 | Whether your existing nuts, and the holes or slots they bear on, work. Metric coarse only in the standard’s table. |
| Material and grade | not in the standard | Corrosion resistance and load-carrying behaviour. Must match whatever the original callout specified. |
| Mechanical requirements | not in the standard | Whether a property class, a proof load or a working load applies, and whether the substitute can evidence it. |
| Coating | not in the standard | Service life in the environment, and the friction and torque behaviour of the joint. |
| Nuts and washers | supplied separately | Whether the assembly is being bought from two documents without anyone owning the interface. |
| Form | A or B | Whether one or both legs are threaded, which fixes the nut count and whether one-sided tightening is possible. |
What this looks like on one size
Take DIN 3570 size 120, the M16 size for DN 100 pipe. The standard’s entry gives a pipe outside diameter of 108 to 114.3 mm, a thread of M16, a minimum thread length of 60 mm, a leg centre distance of 136 mm and an overall height of 171 mm — the full set of values for every size is in the DIN 3570 size chart. For a proposed replacement to be interchangeable at this position, all of the following have to hold: the pipe it goes round measures inside the covered outside diameter range; the inside width of the U clears that pipe; the leg centres land in the support holes at 136 mm; the thread is M16 coarse, with at least 60 mm of thread on each leg in Form A and, in Form B, at least that on the long threaded leg while the shortened leg is matched on its own geometry; the bar diameter and the bend geometry give at least the strength and the seating of the part being replaced; an overall height of 171 mm fits the clearance available; and the material, grade and coating meet the original callout. One of those falling short makes it a different part, even if the other seven agree.
Why pipe size and thread diameter are not enough
Two shortcuts cause most of the problems, and both become obvious once the underlying dimensions are separated.
A nominal pipe size is not an outside diameter. DN is a reference designation: ISO 6708 defines it as an alphanumeric size designation made of the letters DN followed by a dimensionless whole number that is only indirectly related to the bore or to the outside diameter of the pipe ends. One DN can therefore correspond to more than one metric outside diameter, depending on which pipe standard the tube was made to. DN 20 pipe, for example, is 25.0 mm outside in the seamless series and 26.9 mm in the threaded-tube series — and size 30 in DIN 3570 is specified for pipe of exactly that 25 to 26.9 mm range, because both fit. A U-bolt sized on one series is a looser or tighter fit on the other, which is the whole reason the standard lists d1 as a range for the smaller sizes instead of a single number. The DN, NPS and outside-diameter table is the quickest way to establish which series a DN points to before any comparison is made.
A thread diameter is not a shank diameter, and a catalogue column is not necessarily either. DIN 3570 tabulates the shank diameter d2 separately from the thread d3, and the two are not the same number — about 8.9 mm of bar carries an M10 thread, 14.6 mm carries an M16. Published tables handle this inconsistently. One widely copied table prints a “D2” column reading 10, 12, 16, 20 alongside a “D3” column reading M10, M12, M16, M20; the D2 figures there are the thread, not the bar. If you are checking whether the bolt passes through a hole, seats in a saddle, or matches the stiffness of the original, reading the wrong column silently changes the answer.
The substitution risks that actually send a part back
These are the mismatches that come up in practice once a replacement has been proposed from another standard. Each one is checkable, and each one is a reason to go back to the drawing rather than to accept the substitute.
| Risk | What it looks like | What settles it |
|---|---|---|
| Thread system | A metric-threaded DIN 3570 U-bolt is offered an inch-series bent bolt. The nominal diameters are close enough to look convincing on a stock list — an M10 leg against a 3/8″ thread — but the two thread systems do not mate, so the nuts and washers from the original assembly will not run on. | A thread gauge or pitch check on the leg, plus a check of what the mating nuts are. This one is decided immediately. |
| Pipe outside diameter series | The replacement’s size ladder was built for a different OD series. The bolt either grips or rattles, and no amount of tightening changes which. | Measure the pipe. Where it is inaccessible, take the OD from the pipe standard and the pipe marking rather than from the DN. |
| Shank diameter and the “d2” column | The replacement’s data sheet gives one diameter per size, so the shank and the thread cannot be separated from the document alone. A substitution that changes the bar changes stiffness and the fit in the hole. | Ask for the bar diameter and the thread as separate lines, and check both against the drawing. |
| Leg spacing and height | Leg centres that do not align with the support holes, or an overall height that either does not reach the bracket or fouls the structure above. These are the dimensions a drawing review catches and a stock swap does not. | Measure the existing support and the clearance. Compare against e and h1 for the size. |
| Thread length | b is a minimum on the threaded leg or legs. In Form A, both legs are threaded and both have to carry it. In Form B, only the long leg is threaded and only that leg is compared with b; the shortened leg is unthreaded and is checked on its geometry and length instead. If the support plus washer plus nut is thicker than the thread available on the threaded leg, the joint cannot be tightened even though the bolt fits everywhere else. | Add up the stack on the drawing and compare with b on the threaded leg. A longer-thread variant is a different product, not the same one. |
| Material, grade and coating | DIN 3570 leaves all three open. A replacement quoted to a general “steel U-bolt” description can arrive in a different grade, or plain where the original was galvanised, and the corrosion life of the support changes with it. | Compare against the original callout, not against the default the supplier carries in stock. |
| Nuts and washers | The standard supplies the U-bolt alone. Form A and Form B also take different numbers of nuts, so a substitution that switches form changes the bill of materials as well as the part. | Confirm what the original assembly included, and confirm the nut count and washer arrangement for the proposed form. |
| Form A against Form B | One leg is threaded and one is shortened. The parts are not interchangeable — the second leg has no thread, and the height on that side is not h1. | Read the form from the drawing and match it. If access allows tightening from one side only, Form B is the requirement, not a preference. |
When the substitution needs engineering approval
A U-bolt is a simple part carrying a decision that is not always simple. The dividing line is what the bolt does in the installation, not how easy it is to swap.
- Treat it as a drawing change, not a purchasing substitution, where the U-bolt carries load rather than only positioning the pipe — hanger and support design, anything with a calculated load, a specified proof load or a required working load.
- The same applies where the support system is governed by a piping or support code, where the pipe is part of a pressure boundary, or where the installation is fire-rated, offshore, marine or otherwise subject to third-party approval.
- Escalate if the thread changes system, even where the diameter looks the same. It forces a change to the mating nuts and often to the holes or slots they bear on, so more than one part of the assembly moves.
- Escalate if the coating or material changes and the support is in a corrosive or high-temperature environment. Corrosion life and, for some coatings, the friction behaviour of the tightened joint are design inputs there, not finish preferences.
- A size-for-size check is normally enough where the U-bolt is the simple, economical hold-down for a subordinate fixing that it is designed to be — an existing pipe run, an unchanged support, a fastener of the same diameter, thread and geometry, and no load calculation behind it.
A cross-reference procedure that produces a defensible answer
- Get the standard text for the proposed replacement. Not a catalogue page and not a summary. The scope paragraph alone will tell you whether it covers the part at all — inch against metric, bent bolts against hanger selection, product standard against application standard.
- Build the same list of data points for the replacement — every row of the dimensional table above, including the three the standard does not cover. Where the other document does not state one, record it as not stated rather than assuming it matches.
- Measure the pipe and the support. Outside diameter, clearance above the pipe, hole pitch, hole diameter and the thickness of everything the legs pass through.
- Check the thread first. It is the one dimension that decides the question on its own, and it is the one most often skipped because the diameter looks familiar.
- Check the three dimensions that bracket the pipe: inside width, leg centre distance and overall height. A part that fails any of these cannot be made to fit by tightening it differently.
- Confirm the unstated items separately — material, grade, mechanical requirements, coating, and whether nuts and washers are included. These are where a substitution quietly changes what was bought.
- Decide who signs it off. If the part carries load, sits under a code or will be inspected by someone else, the answer is engineering rather than purchasing. Record the check either way, so the next person can see what was compared and against which edition.
Where that leaves the equivalence question
There is no DIN 3570 equivalent to look up. There is a documented standard, unchanged since 1968 and still in force, and there is a market full of U-bolts built to other standards that will do the same job when they match on pipe outside diameter, inside width, leg centres, bar diameter, bend geometry, height, thread length, thread, material, coating and the parts that come with them. Matching the pipe size or the thread diameter alone answers none of that, and a change of standard is a change to the specification the drawing cited — which is why a paper check on the dimensions and, where the bolt carries load, an engineering signature belong in the process before the order is placed.
ChinaBolts is a fastener manufacturer and supplier, and DIN 3570 U-bolts are part of the range we quote. Tell us the pipe outside diameter, the size and thread you need, the form, the material and coating, and the dimensions the replacement has to match.
We will confirm what we can supply against the actual specification, and where a proposed alternative does not line up, we will tell you.
