Bend steel pipe UK: bore, wall and the stops
Updated: 23 October 2026
The tube on the rack says 15 mm, the die in the box says 1/2 inch, and a 12 ton frame looks as if it will settle the argument. If you want to bend steel pipe UK workshops actually stock, you match nominal bore, outside diameter and wall to the listing, and you treat gas installation pipework as Gas Safe work. A 15 mm mark is not a 15 mm outside diameter. Medium wall can sit under the 2.75 mm floor printed on the KATSU page even when the die number looks right. Copper lever benders are a different category. Peter F. used BS EN 10255 datasheets, the amazon.co.uk listings and the gas-safety rules, as read on 22 October 2026. We did not bend a sample. Our [pipe bending machine comparison](/hub/diy-supplies/pipe-bending-machine) holds the machines. A purchase through our links can earn a commission at no extra cost to you.
The tube on the rack says 15 mm, the die in the box says 1/2 inch, and a 12 ton frame looks as if it will settle the argument.
The tube on the rack says 15 mm, the die in the box says 1/2 inch, and a 12 ton frame looks as if it will settle the argument. If you want to bend steel pipe UK workshops actually stock, you match nominal bore, outside diameter and wall to the listing, and you treat gas installation pipework as Gas Safe work. A 15 mm mark is not a 15 mm outside diameter. Medium wall can sit under the 2.75 mm floor printed on the KATSU page even when the die number looks right. Copper lever benders are a different category. Peter F. used BS EN 10255 datasheets, the amazon.co.uk listings and the gas-safety rules, as read on 22 October 2026. We did not bend a sample. Our pipe bending machine comparison holds the machines. A purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Stated wall | Die range | Thin-wall copper | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  WINMAX TOOLS AUTOMOTIVE WINMAX manual tube bender, 1 in to 3 in | n/a | 7 dies; 6 circular from 1 in to 3 in | Not stated. One US review mentions sand-filled copper | 1.8 | about £199.96 | View offer |
 KATSU Tools KATSU 12 ton hydraulic pipe bender, 6 dies | 2.75 mm to 4.5 mm | 6 dies, 1/2 in to 2 in BSP | Not suitable | 6.4 | about £119.99 | View offer | |
 DRAUXI DRAUXI manual rolling machine, TR40 | n/a | n/a | n/a | 0.2 | about £345.79 | View offer |
On this page
What 15 mm steel pipe actually measures
Nominal bore is the name of the pipe, not the width of the metal you put in the die. Palmer’s datasheet for BS EN 10255 puts 15 mm, also called 1/2 inch, at 21.3 mm outside diameter, and 50 mm, called 2 inch, at 60.3 mm outside. CMT’s sheet uses those same outside diameters. You are bending a tube a little over 21 mm across, not a 15 mm copper pipe. BS EN 10255:2004, on the BSI scope note, covers non-alloy steel tubes from 10.2 mm to 165.1 mm outside, in medium and heavy series.
Hilka’s 12 tonne bender prints roller settings of 21.25 mm, 26.75 mm, 33.50 mm, 42.25 mm, 48 mm and 60 mm. Those figures sit on the BS EN 10255 outside diameters, so a BSP die is not a former for 15 mm copper. Clarke says the same class of machine is for steel, not thin-wall copper. If your tube measures about 21.3 mm outside, you are in the 1/2 inch steel conversation. If it measures 15 mm outside, the steel die is the wrong shape. How to choose ram, former or roll is the pipe bending machine buying guide.
Medium wall and the 2.75 mm line
Wall thickness decides whether the KATSU listing even claims the tube. That page prints 2.75 mm to 4.5 mm. Palmer gives 15 mm medium wall as about 2.65 mm and heavy as about 3.25 mm. CMT rounds the same sizes to 2.6 mm and 3.2 mm. Both put medium 15 mm under 2.75 mm. Medium wall at 20 mm nominal bore is about 2.6 mm as well, so that size misses the same floor. Heavy 15 mm, about 3.25 mm on Palmer’s sheet, sits inside the printed band.
Palmer gives 2 inch tube an outside diameter of 60.3 mm, medium wall about 3.65 mm and heavy wall 4.50 mm. CMT rounds those walls to 3.6 mm and 4.5 mm. Medium 2 inch is inside the KATSU range. Heavy 2 inch sits on the 4.5 mm ceiling. A medium 15 mm tube can still be forced through a ram. It is simply outside the wall the listing states, so expect an oval bore or a kink. Heavy series at 15 mm is the closer paper match, and you still check the wall with a calliper.
Copper, conduit, gas and cast steel
The KATSU listing, Clarke and Hilka all say this steel bender is not for thin-wall copper. BS EN 1057 copper needs a former made for that outside diameter. A 15 mm or 22 mm heating pipe in a 1/2 inch BSP die is the wrong combination, even when the ram is strong enough to crease it. Water fittings in England and Wales have to stay workmanlike under the Water Supply (Water Fittings) Regulations 1999. Do not apply those 1999 regulations to Scotland or Northern Ireland, which have their own rules.
One KATSU review says electrical metallic conduit flattened. That is a single review, not a laboratory test, and this page does not invent a conduit standard the listing never cites. The pump sequence, once the steel is in range, is the how to use a hydraulic pipe bender page. A die stamped for gas-specification pipe is not permission to alter a gas installation. Regulation 3 of the Gas Safety (Installation and Use) Regulations 1998 requires competence for gas fitting work. Employers and the self-employed must be in the class approved by the Health and Safety Executive, which in practice is Gas Safe registration. Cast steel is a separate stop. The Frank Key hire leaflet tells you not to bend it, because it can shatter. Which listing states the 2.75 mm line is on the best pipe bender UK page.
Measure the wall, then decide who bends it
Match 15 mm or 1/2 inch steel to about 21.3 mm outside, then check the wall against 2.75 mm to 4.5 mm. The KATSU ram is the top pick and the best value in this set when that wall is inside the printed band. Medium 15 mm and 20 mm at about 2.6 mm are under the floor. Gas installation pipework stays with a Gas Safe engineer, and cast steel stays out of the ram. The awards rank only these three stored listings.
Common questions
Will a 1/2 inch die bend 15 mm steel pipe?
It is the same nominal size. Palmer lists 15 mm and 1/2 inch at 21.3 mm outside diameter, so the die is aiming at that outside, not at 15 mm across the metal. The bend is only inside the KATSU claim if the wall is at least 2.75 mm. Medium wall, about 2.65 mm on Palmer’s sheet, is under that line. Heavy wall, about 3.25 mm, is inside it. Measure before you pump.
Is medium-wall 15 mm tube inside a 2.75 mm minimum?
No. Palmer’s medium wall for 15 mm is about 2.65 mm, and CMT rounds the same tube to 2.6 mm. Both are under the 2.75 mm floor on the KATSU listing. Medium 20 mm is described at about 2.6 mm as well. That does not mean the ram cannot move the pipe. It means the listing does not claim this wall, and you should expect ovality or a kink.
Can I bend copper heating pipe on the same machine?
Not on the steel ram these pages describe. KATSU, Clarke and Hilka exclude thin-wall copper. BS EN 1057 tube needs its own former. A 15 mm copper pipe is not 15 mm nominal-bore steel, and a BSP die will flatten it. In England and Wales a water fitting still has to be workmanlike. Scotland and Northern Ireland are not covered by the 1999 English and Welsh regulations.
Will it bend electrical conduit?
Do not plan on it. One KATSU review says electrical metallic conduit flattened in this class of die. That is one report, not a test, and no conduit standard is printed on the listing. A crushed bore is a failed bend. Use a bender sold for the conduit you have, rather than a 12 ton frame set up for heavy steel tube.
Can I bend pipe for a gas boiler myself?
No. Work on gas fittings and installation pipework has to be done by someone competent, and employers and the self-employed need to be in the HSE-approved class, which in practice means Gas Safe registration. Regulation 3 of the Gas Safety (Installation and Use) Regulations 1998 is the rule. Buying or hiring a 12 ton bender does not change it. A householder does not alter the boiler pipe with a ram.
What is the outside diameter of 2 inch steel tube?
Palmer and CMT both give 2 inch BS EN 10255 tube an outside diameter of 60.3 mm. Medium wall is about 3.65 mm on Palmer’s sheet and about 3.6 mm on CMT’s. Heavy wall is 4.50 mm. The KATSU range runs to 4.5 mm, so heavy 2 inch is on the limit. Galvanised and black tube of that nominal bore use the same die. The coating does not change the outside diameter.
What about cast iron or cast steel?
Do not bend cast steel in this ram. The Frank Key hire leaflet says it can shatter. The same sources do not give a safe method for cast iron, so you do not trial that either. These machines are aimed at ductile steel tube with a wall the listing accepts. Brittle cast metal is a stop, in the same way a gas fitting is a stop, even when the piece happens to sit in the die.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Listings captured 21 October 2026. Updated 23 October 2026.
- HSE: PUWER overview (retrieved 23 October 2026)
- HSE: EIS7 three-roll bending machines (retrieved 23 October 2026)
- Supply of Machinery (Safety) Regulations 2008 (retrieved 23 October 2026)
- Yorkshire Copper technical guide (retrieved 23 October 2026)
- Lawton: how to bend plumbing copper tube (retrieved 23 October 2026)
- Palmer: BS EN 10255 carbon steel tube (retrieved 23 October 2026)
- Water Supply (Water Fittings) Regulations 1999 (retrieved 23 October 2026)
- Gas Safety (Installation and Use) Regulations 1998 (retrieved 23 October 2026)