Round Bend U Bolt for Pipe Clamp DIN 3570 Carbon Steel DN20-DN500

Product Description

Product Description

Product Overview

Fasto U-bolts are cold bent from round steel bar into a U shape with threaded legs, used to clamp pipe, round bar, profile steel and spring plate onto brackets, supports or flat plates. Each U-bolt is normally used as a set of one U-bolt plus two nuts, with washers added where required. Dimensions follow DIN 3570:1968-10 for the metric series (NW 20 to NW 500) and ASME B18.31.5-2011 (R2016) for the inch series, with round bend, square bend and semi-round forms available. The standard material is S235JR carbon steel to DIN EN 10025-2; property classes 4.6, 4.8 and 8.8 to ISO 898-1 and stainless steel A2-70, A4-70 and A4-80 to ISO 3506-1 are produced on request. Finish options include plain, zinc plating to ISO 4042 and hot dip galvanizing to ISO 1461 for outdoor and coastal service. The size range covers inner width a from 30 mm to 530 mm (DN 20 to DN 500), and inch sizes from 1/4 in. to 1-1/8 in. UNC for NPS 1/2 to NPS 24. Custom leg length, thread length, material and finish are available for OEM projects.

Specifications

Item	Value
Standard	DIN 3570:1968-10 (Metric, NW 20 - 500); ASME B18.31.5-2011 (R2016) Bent Bolts Inch Series
Bend Form	Round bend (semi-circular) / Square bend (two 90 degrees) / Semi-round; DIN 3570 Form A and Form B
Leg Type	Form A: both legs equal and threaded; Form B: one leg shortened, single side locking
Material	S235JR carbon steel (DIN EN 10025-2); stainless A2-70 / A4-70 / A4-80 (ISO 3506-1); classes 4.6 / 4.8 / 8.8 (ISO 898-1) on request
Size Range (Metric)	DN 20 - DN 500; inner width a 30 mm - 530 mm
Size Range (Inch)	NPS 1/2 - NPS 24; thread 1/4 in. - 1-1/8 in. UNC (UNF on request)
Thread	Metric ISO 724 / ISO 965-2, class 6g; inch UNC per ASME B1.1
Rod Diameter d2	8.9 / 10.7 / 14.6 / 18.2 / 21.9 mm for M10 / M12 / M16 / M20 / M24
Thread Length b	Minimum values per standard (40 - 70 mm over the range); longer thread on request
Surface Treatment	Plain / Zinc plated (ISO 4042) / Hot dip galvanized (ISO 1461) / Black oxide
Companion Parts	Hex nuts DIN ISO 4032 and pipe clamps DIN 3567 supplied separately on request
Inspection	Thread GO-NOGO gauge per ISO 1502; surface defects per ISO 6157-1
Documents	EN 10204 3.1 material test certificate with traceability
OEM Service	Custom leg length, thread length, material, finish and private label packing

DIN 3570 Form A reference dimensions (mm) - round bend, both legs equal and threaded. Inner width a must match the pipe outer diameter d1; e is the outer width over the bend; b is the minimum thread length; h is the overall height.

Nominal Size	Pipe OD d1	Inner Width a	Outer Width e	Thread d3	Rod Dia d2	Thread Length b min	Height h
DN 20 (3/4 in.)	25 - 26.9	30	40	M10	8.9	40	70
DN 25 (1 in.)	30 - 33.7	38	48	M10	8.9	40	76
DN 32 (1-1/4 in.)	38 - 42.4	46	56	M10	8.9	50	86
DN 40 (1-1/2 in.)	44.5 - 48.3	52	62	M10	8.9	50	92
DN 50 (2 in.)	57 - 60.3	64	76	M12	10.7	50	109
DN 65 (2-1/2 in.)	76.1	82	94	M12	10.7	50	125
DN 80 (3 in.)	88.9	94	106	M12	10.7	50	138
DN 100 (4 in.)	108 - 114.3	120	136	M16	14.6	60	171
DN 125 (5 in.)	133 - 139.7	148	164	M16	14.6	60	191
DN 150 (6 in.)	159 - 168.3	176	192	M16	14.6	60	217
DN 175 (7 in.)	191 - 193.7	202	218	M16	14.6	60	249
DN 200 (8 in.)	216 - 219.1	228	248	M20	18.2	70	283
DN 250 (10 in.)	267 - 273	282	302	M20	18.2	70	334
DN 300 (12 in.)	318 - 323.9	332	352	M20	18.2	70	385
DN 350 (14 in.)	355.6 - 368	378	402	M24	21.9	70	435
DN 400 (16 in.)	406.4 - 419	428	452	M24	21.9	70	487
DN 500 (20 in.)	508 - 521	530	554	M24	21.9	70	589

Sizes outside the DIN 3570 native range (for example DN 15 or DN 600) are produced as extensions of the standard and are confirmed by measured drawing before order. Dimensions of the inch series follow the ASME B18.31.5 tolerance tables; the commercial inch sizes most often ordered are shown below (NPS 1/2 to NPS 24, all dimensions in inches).

Nominal Pipe Size	Inner Width A	Inner Length C	Thread Diameter D	Thread Length B
1/2	7/8	2-1/4	1/4	3/4
3/4	1-1/8	2-1/2	5/16	7/8
1	1-3/8	2-3/4	5/16	7/8
1-1/2	2	3-1/4	3/8	1
2	2-1/2	3-3/4	3/8	1
3	3-5/8	4-3/4	1/2	1-1/4
4	4-5/8	5-3/4	1/2	1-1/4
6	6-3/4	7-3/4	5/8	1-1/2
8	8-3/4	9-3/4	3/4	1-3/4
12	12-7/8	14	7/8	2
16	16-1/8	17-1/2	1	2-1/4
24	24-1/8	25-1/2	1-1/8	2-3/4

Features & Advantages

• Round bend and square bend produced to the correct form, so the clamp matches the clamped part and avoids four-point contact, corner crushing or pipe ovalisation.
• Inner width a matched to the actual pipe outer diameter, confirmed with the customer before production - no nominal-size guessing.
• Round bar diameter follows the standard for every thread size (8.9 mm / 10.7 mm / 14.6 mm / 18.2 mm / 21.9 mm for M10 / M12 / M16 / M20 / M24), rolled to ISO 724 / ISO 965-2 class 6g threads.
• Full metric range DN 20 - DN 500 in one supply, plus inch series NPS 1/2 - NPS 24, with mixed sizes and finishes consolidated into one shipment.
• Material and finish matched to the working environment: S235JR carbon steel, classes 4.6 / 4.8 / 8.8, stainless A2-70 / A4-70 / A4-80; plain, zinc plated or hot dip galvanized.
• Heavy corrosion protection for coastal and outdoor pipe work with hot dip galvanizing to ISO 1461 and neutral salt spray testing to ISO 9227 on request.
• Factory direct with full quality control from raw bar to packing; thread gauge, dimensional and surface defect records plus an EN 10204 3.1 material test certificate with each shipment.
• OEM / ODM service: custom leg length, thread length, material, finish and private label packing for contractors and brand owners.

Standards & Installation

DIN 3570:1968-10 is the metric standard for round steel U-bolts for pipes from NW 20 to NW 500 and specifies inner width a, outer width e, thread d3, rod diameter d2, minimum thread length b and height h. The inch series is covered by ASME B18.31.5 for bent bolts, with UNC threads per ASME B1.1 as the default and UNF on special order. Rod diameter d2 is always smaller than the thread diameter d3 because the thread is rolled from the finished bar: 8.9 mm for M10, 10.7 mm for M12, 14.6 mm for M16, 18.2 mm for M20 and 21.9 mm for M24. Thread length b is a minimum value, so a longer thread is compliant but reduces the effective clamping travel for the same weight.

Selection rule: use a round bend for round pipe and a square bend for square tube, and always order by pipe outer diameter rather than nominal size. When measuring a bent bolt in goods receipt, the inner width of a square bend U-bolt must be checked at half of the inner length, because spring-back makes the width vary along the legs. Installation requires enough leg length to cover the clamped part, the bracket plate thickness, the washer, the nut height and about two thread pitches of exposed thread; DIN 3570 does not set a separate tolerance for leg length, so this is agreed in the order specification. Tolerances not listed in DIN 3570, such as deviations of inner width a, height h, the distance between leg axes and the squareness of the leg ends, can be specified to your drawing, using the ASME B18.31.5 tolerance table as a magnitude reference.

A U-bolt is a simple piece of hardware with an unusually wide reach. Two threaded legs, one bend, and a pair of nuts - and the same basic geometry turns up holding a process pipe to a steel rack, pinning a leaf spring to an axle housing, and keeping a wire rope from slipping through a grip.

Pipe support is where U-bolts are most thoroughly standardised. In Europe, DIN 3570 defines the clamp geometry for pipe outside diameters from roughly 20 mm up to 520 mm, normally produced in S235JR steel accepted for service up to 300 °C, with zinc-plated, hot-dip galvanized and stainless versions for aggressive plant environments. North American practice covers the same duty through MSS SP-58 Type 24, bolting the pipe against a structural member. Both routes obey the same first rule: inside width has to match the pipe outside diameter, and the bend has to seat flat against the load.

Automotive work is a different animal. When a U-bolt clamps a leaf spring pack onto an axle, it lives with constant flexing and road shock, so the specification shifts to SAE J429, most often Grade 5 or Grade 8 depending on the load the suspension is asked to carry. Rigging follows yet another rulebook: U-bolt wire rope grips form eye terminations on steel wire rope and are governed by EN 13411-5, with DIN 741 as the familiar European equivalent. Beyond these three, U-bolts show up on utility poles and sign structures, in marine and offshore fittings where 316 stainless is the default choice, and on solar mounting rails where galvanized carbon steel still wins on cost.

One caution applies everywhere. Only the two legs carry load - the bend is a locating feature, not a strength feature. Sizing leg diameter by how substantial the U looks, rather than by the tensile area of the threaded legs, is the mistake that fails first.

Quality Control

Production is controlled from raw bar to packing: incoming steel is checked against the mill certificate, bars are cut and bent to the drawing, threads are rolled and checked with GO-NOGO gauges to ISO 1502, and surface defects are inspected to ISO 6157-1 before final quality control and packing. Material traceability is maintained for each batch, and an EN 10204 3.1 material test certificate is issued with the shipment.

Packaging & Delivery

Export packing options are cartons for small and mid-size orders, woven bags for bulk standard sizes and wooden pallets for heavy and export shipments, with long legs bundled by size for stable container loading. Plain parts are lightly oiled and galvanized parts are separated to protect the coating during sea transit. Free samples are dispatched within 7 days. Stock sizes (DN 20 - DN 150 common) dispatch in 7-10 days, and production orders are ready in 15-25 days depending on size and quantity; full container loads take 20-30 days. MOQ is 500 pieces or 200 kg, mixed-size trial orders are accepted, and price terms are FOB, CFR, CIF, DDP or DAP.

About Fasto & Factory Strength

Fasto is a professional fastener manufacturer and exporter founded in 2005 and registered in Xi'an, China. Two production bases serve global orders: the Tianjin plant for carbon steel and stainless steel fasteners, and the Chongqing plant for bimetal screws; the sales and foreign trade team is based in Xi'an. Factory area exceeds 5,000 square meters with a monthly capacity of more than 800 tons, exporting to 128 countries with 74,000+ online transactions and 3,000+ successful project cases. Quality is controlled under the ISO 9001:2015 quality system (WSF issued, CNAS/IAF accredited), with IATF 16949 applied as the internal multi-process control standard. Alongside U-bolts, the product range covers hex bolts, flange bolts, carriage bolts, T-bolts, socket head cap screws, hex nuts, washers, anchors, rivets and bimetal self-drilling screws, so a full pipe support and structural fastening package can be consolidated into one order.
Since 2013 Fasto has exhibited at domestic and international hardware and fastener trade shows, and in 2025 established a subsidiary (LLC) in Saudi Arabia to serve Middle East customers directly. Company milestones: the second production base was built in 2008, multiple international certifications were obtained in 2015, and a new modern office building was completed in 2024. Supplier qualifications include the SGS Gold Plus Supplier Assessment and CE certification for bimetal screws (EN 14568), with SGS material traceability on every batch. A multilingual sales team (English, French, Spanish, Arabic, Russian) replies to inquiries within 12 hours and provides quotations within 24 hours.