How-to · Tube fittings
Compression and bite-type fittings: how many turns, how to check, what goes wrong
How many turns a new fitting needs, how to tell it is made up correctly, and why re-tightening allows only 30° to 90°. With the assembly instructions of five manufacturers compared.
Contents
For a new two-ferrule compression fitting up to 1 in (25 mm): finger-tight, then 1¼ turns. A DIN bite-type fitting (ISO 8434-1) usually needs 1¼–1½ turns from first contact; after that, every re-make-up is only 30–90° past the torque rise 3, 4, 6, 8.
- Small two-ferrule sizes (2–4 mm and 1/16–3/16 in) take only ¾ turn 8. One bite-type maker, Schwer, specifies 1–1¼ turns 7.
- Check: on bite-type fittings a visible collar must cover at least 80 % of the front cutting edge; on two-ferrule fittings the gap gauge must not enter (initial make-up only) 4, 6, 9.
- Cut the tube square and deburr it, never put tape on the ferrule; soft copper and plastic tubing need an insert or support sleeve 4, 6, 10.
- “¼–½ turn past hand-tight” is a re-tightening value, not an initial make-up value: it is only 17–50 % of the required travel 13.
Key terms in 30 seconds
- Two-ferrule fitting
- A compression fitting with two rings, a front and a back ferrule, used in instrumentation. Sizes and make-up are set by the manufacturer.
- Olive / brass compression ring
- A soft ring, usually brass, that squeezes around the tube without cutting. Common on copper. Also sold as a “compression sleeve”.
- Bite-type fitting
- A ring with sharp edges that the nut pushes onto a cone. It bites into the tube and holds it. Standardised as DIN 2353 / ISO 8434-1.
- 24° cone
- The cone-shaped seat in the fitting body that the ring is pressed into. Standardised in ISO 8434-1.
- Initial make-up / pre-assembly
- The first tightening of a new fitting: usually 1¼ to 1½ turns from first contact. That is when the ring bites in.
- Final make-up / re-make-up
- Tightening after loosening: until it gets noticeably harder, then only 30° to 90° more.
- Collar
- A small ridge of tube material in front of the cutting edge. It shows the ring has bitten in properly.
- Insert / support sleeve
- A sleeve inserted into the tube so soft tubing (copper, plastic) does not collapse when tightened.
A new two-ferrule fitting gets 1¼ turns from finger-tight; a new DIN bite-type fitting gets 1¼ to 1½ turns from first contact, is opened to check the collar and is then tightened to the torque rise plus 30–90°. The exact figure is in your manufacturer’s instructions; the table in the mini study compares five makers. For finding such values, see Reading data sheets correctly.
Important: never tighten a fitting while the line is under pressure. The manufacturer calls this a danger to life 3. Depressurise the line first.
Two-ferrule, olive or bite-type: what is what?
In the US, “compression fitting” mostly means one of two things: a brass olive on copper or PEX in plumbing, or a two-ferrule fitting in instrumentation. The third type, the bite-type fitting, is the European hydraulic standard: a 24° cone to ISO 8434-1 1, often still called DIN 2353. DIN 2353 remains current alongside it and covers complete fittings with stud ends to DIN 3852 that ISO 8434-1 does not include 2. The threads of these stud ends are listed in our thread chart.
The two cut-away drawings below show a bite-type fitting before and after tightening.
- This is a section: the fitting is cut open lengthwise so you can look inside.
- The numbers: 1 fitting body with stud thread (left), 2 union nut, 3 cutting ring (red), 4 tube.
- Before tightening, the cutting ring sits loosely on the tube and the nut is only screwed on.
- The same section after tightening, with the same numbers.
- The nut (2) has pushed the cutting ring (3) into the cone of the body (1). Its front edge has pressed into the tube (4).
- Look at the red ring: before it sat loosely, now it is wedged between cone and tube.
| Type | How it holds the tube | Tube | Standard | Initial make-up | Check afterwards |
|---|---|---|---|---|---|
| Two-ferrule fitting | front and back ferrule are pressed onto the tube | instrumentation tubing, metric and inch | manufacturer’s own standard | 1¼ turns from finger-tight, 2–4 mm only ¾ 8 | gap inspection gauge, initial make-up only 8, 9 |
| Brass olive (plumbing compression fitting) | soft brass ring is squeezed, does not cut | copper tube in building services; soft tube with support sleeve | EN 1254-2 12 | per manufacturer’s instructions | per manufacturer |
| Bite-type fitting 24° | ring bites into the tube and raises a collar | steel and stainless tube; copper and plastic with support sleeve | ISO 8434-1 1, DIN 2353 2 | usually 1¼–1½ turns from contact, Schwer 1–1¼ 3, 4, 6, 7 | collar covers ≥ 80 % of the edge 4, 6 |
Make-up instructions apply only to the parts of that manufacturer. Never mix ferrules, nuts and bodies from different brands 8, 10.
Bite-type series LL, L and S
Bite-type fittings come in three series: LL, L (light) and S (heavy). The series sets the nut thread and the pressure rating. One manufacturer gives these ratings for steel:
| Series | Tube outside diameter | Pressure rating (manufacturer, steel) |
|---|---|---|
| LL | see data sheet | PN 100 (≈ 1,450 psi) |
| L | 6–18 mm | PN 315 (≈ 4,570 psi) |
| L | 22–42 mm | PN 160 (≈ 2,320 psi) |
| S | 6–14 mm | PN 630 (≈ 9,140 psi) |
| S | 16–30 mm | PN 400 (≈ 5,800 psi) |
| S | 38 mm | PN 315 (≈ 4,570 psi) |
Manufacturer data for union nuts to ISO 8434-1/DIN 3870, retrieved 2026-11-02 11. We have not seen the pressure table of the standard itself. The permitted pressure depends on size, material and manufacturer and is stated in the data sheet. 1 bar = 14.5 psi.
Two-ferrule compression fittings (instrumentation)
Instrument and sample lines often use two-ferrule fittings with a front and a back ferrule. For sizes up to 1 in (25 mm) Swagelok specifies 1¼ turns from finger-tight; for 1/16 to 3/16 in and 2 to 4 mm only ¾ turn 8, 10.
Clock trick: mark the nut at 6 o’clock. One full turn brings the mark back to 6, another quarter turn to 9 o’clock: that is 1¼ turns.
A gap inspection gauge between the nut and the body hexagon shows whether the fitting is tight enough: if the gauge will not enter the gap, the travel is right. The gauge applies to the initial make-up only and only with parts from the same manufacturer 8, 9.
For re-make-up, turn the nut to its previous position, where torque rises noticeably, then tighten slightly. The instructions name no sealant on the ferrule, and parts from other manufacturers are excluded 10.
Preparation: cut, deburr, insert the sleeve
Many faults happen before the nut is even started. For bite-type fittings on steel and stainless tube, Parker, VOSS and HANSA-FLEX give these steps:
1. Cutting: saw the tube square, no more than ±0.5° (HANSA-FLEX) or ±1° (VOSS) out. Wheel cutters and abrasive cut-off saws are ruled out 3, 4, 6.
2. Deburring: deburr lightly inside and outside, chamfer no more than 0.3 mm × 45°, remove chips 3, 6.
3. Straight tube end: the tube must be straight for at least twice the nut height in front of the fitting 3.
4. Sleeve: soft copper and plastic tube need a support sleeve in the tube end, thin-walled steel tube as the manufacturer specifies. Reinforcing sleeves are tapped in before assembly 4, 6.
5. Lubrication: oil the thread and ring, use grease instead of oil on stainless 6. No tape or hemp on the ring or cone: the seal is made at the ring itself 6, 10.
6. Stainless: pre-assemble stainless cutting rings only in a hardened pre-assembly body; pre-assembly in the fitting body is not permitted 3, 6.
- The parts are laid out from left to right in the order they are assembled.
- On the left the plastic tube with the support sleeve in its end. The sleeve is orange here only to make it stand out.
- Next come the union nut and the cutting ring. The narrow, tapered end of the ring points towards the body, i.e. towards the tube end.
- On the right the fitting body with the thread for the nut and the stud end.
Bite-type fittings step by step
These steps are for direct assembly in the fitting body, i.e. steel tube in small sizes. The instructions of the manufacturer whose parts you install always take precedence.
Direct assembly in the fitting body
1. Slide the nut and the cutting ring onto the tube. The cutting edge of the ring points towards the tube end.
2. Push the tube into the body up to the shoulder and hold it there.
3. Screw the nut on by hand until it clearly seats. Count from here.
4. Mark the nut and the tube with a line. That way you can count the turns reliably.
5. Tighten with a spanner by 1½ turns, 1¼–1½ depending on the manufacturer (Schwer 1–1¼). Counter-hold the body with a second spanner and keep pressing the tube against the shoulder 3, 4, 6, 7.
6. Loosen the nut and check the collar (see below). Then tighten to the noticeable torque rise and apply the final make-up as specified.
- On the left the port block with the screwed-in fitting body; from the right the tube enters the union nut.
- The left spanner holds the body still (counter-holding), the right one turns the nut.
- The orange line on the nut is the mark. Count the turns with it: once all the way round is one turn.
Pre-assembly in a hardened pre-assembly body
Stainless rings are always pre-assembled in a hardened pre-assembly body, by machine from 30 mm tube OD 3, 6. Only then does the tube with the bitten-in ring go into the actual fitting.
Checking the collar
After pre-assembly, loosen the nut and look at the tube: a collar must run all the way round in front of the front cutting edge. VOSS and HANSA-FLEX require it to cover at least 80 % of the cutting edge face; Parker requires it to cover the front of the edge 3, 4, 6.
The ring may rotate on the tube but must not move axially 6. With VOSS Ring M the collar is about 100 %, and a gauge is recommended 5.
- The union nut is pushed back to the left. Next to it on the right sits the cutting ring with its tapered nose.
- Directly in front of the nose a ridge runs around the tube: that is the collar, tube material pushed up by the ring.
- The collar is exaggerated in this picture for clarity. A real collar is smaller; the 80 % criterion in the text is what counts.
- In the background a fitting body with a protective cap.
Final make-up and re-make-up
After the check, screw the nut back on until torque rises noticeably. The final make-up counts only from this point: 30° for Parker EO (new) and VOSS Ring M, 90° for Parker traditional, VOSS 2S and HANSA-FLEX steel, 180° for HANSA-FLEX stainless and 90–180° for Schwer 3, 4, 5, 6, 7. Counter-hold the body.
Every later re-make-up works the same way: up to the torque rise, then only the small angle, never 1½ turns again. Never tighten under pressure 3.
Mini study: turns compared across manufacturers
A rule often found online says to tighten a compression or bite-type fitting “¼ to ½ turn past hand-tight”. We put the assembly instructions of five manufacturers side by side: how far does the nut really have to turn on initial make-up, and how far on final make-up?
- Sample
- 10 make-up instructions from 5 manufacturer documents
- Selection
- bite-type 24° to ISO 8434-1 from Parker, VOSS, HANSA-FLEX and Schwer, two-ferrule fitting from Swagelok; recorded: turns and degrees per step, reference point, check, tube preparation
- Updated
- 2 November 2026
- Limits
- Parker values from the 08/2005 edition, confirmed by the 04/2019 edition; VOSS and Schwer documents undated; each instruction applies only to that manufacturer’s parts
- Each row is one manufacturer’s assembly instruction. Left to right: how far the union nut is turned in total, in degrees. 360° is one full turn.
- The orange part is the initial make-up (when the ring bites in), the aubergine part the final tightening after the noticeable rise in torque.
- Example: Parker (new) specifies 540° (1½ turns) plus 30°, HANSA-FLEX stainless 450° (1¼ turns) plus 180°.
- Almost all orange bars end between 450° and 540°. Exceptions: Schwer specifies 360° to 450° depending on size (the pale part shows the range), Swagelok only 270° for very small 2–4 mm tubes. The often-quoted rule “¼ to ½ turn” (90° to 180°) would be only a short stretch at the start of these bars.
The ten instructions in detail
| Manufacturer and system | Initial make-up | Final make-up after torque rise | Check |
|---|---|---|---|
| Parker EO, optimised | 1½ turns = 540° 3 | 30° | collar covers the front of the cutting edge |
| Parker EO, traditional (DIN 3859-2) | 1¼ turns = 450° 3 | 90° | as above |
| VOSS 2S | 1½ turns up to 18 mm, 1¼ from 20 mm 4 | 90° | collar ≥ 80 % |
| VOSS Ring M | 1½ turns to the positive stop 5 | 30° | collar approx. 100 %, gauge |
| HANSA-FLEX steel, complete make-up | 1½ turns = 540° 6 | – | cutting edge evenly covered |
| HANSA-FLEX steel, pre-assembly | 1¼ turns = 450° 6 | 90° | approx. 80 % covered |
| HANSA-FLEX stainless | 1¼ turns = 450° 6 | 180° | approx. 80 % covered |
| Schwer SR | 1–1¼ turns = 360–450° 7 | 90–180° | tube turns along up to approx. ½ turn, then no longer |
| Swagelok up to 1 in / 25 mm (two ferrules) | 1¼ turns from finger-tight = 450° 8 | – | gap inspection gauge |
| Swagelok 2–4 mm (two ferrules) | ¾ turn = 270° 8 | – | gap inspection gauge |
Turns counted from noticeable contact (Swagelok: from finger-tight). – = no separate final step. For comparison: “¼ to ½ turn past hand-tight” is 90–180°, i.e. 17–40 % of 450–540° (Schwer: 20–50 %) 13.
What does this mean for you? On a new fitting: run the nut on by hand until it seats, then 1½ turns; check the figure for your brand. A mark on nut and tube helps you count. After loosening, never 1½ turns again, but up to the torque rise and then only 30–90°.
Why the final turn is so small
A final make-up of 30° to 90° sounds like very little, and it is. A simple calculation shows how little: with every turn the nut advances by the pitch of its thread 13.
Simply explained: Each full turn moves the nut forward by one thread pitch. Half a turn moves it by half a pitch, a twelfth of a turn by a twelfth.
- s
- travel of the nut along the tube (axial travel) in mm
- φ
- rotation angle of the nut in degrees
- P
- pitch of the nut thread in mm, e.g. 1.5 mm for M12×1.5 (size 6L)
1½ turns on 6L (M12×1.5): 540 / 360 × 1.5 mm = 2.25 mm of travel.
30° final make-up: 30 / 360 × 1.5 mm = 0.125 mm, about the thickness of a sheet of paper. That is why it counts only from the noticeable torque rise, not from “hand-tight”.
| Series and size | Nut thread | Pitch P | 30° | 90° | 180° | 1¼ turns | 1½ turns |
|---|---|---|---|---|---|---|---|
| L 6–18, S 6–16 | M12×1.5 to M26×1.5 | 1.5 mm | 0.125 mm | 0.375 mm | 0.75 mm | 1.875 mm | 2.25 mm |
| L 22–42, S 20–38 | M30×2 to M52×2 | 2 mm | 0.167 mm | 0.5 mm | 1.0 mm | 2.5 mm | 3.0 mm |
Axial travel s = (φ / 360°) · P, own calculation for 19 sizes 13. Nut thread per size from manufacturer data 11. Series LL has finer threads and is not calculated here.
What does this mean for you? “A bit tighter” really is enough on re-make-up, but only if the ring bit in properly the first time. An extra eighth of a turn (45°) is already 2.5 times the intended travel with a 30° instruction (75° instead of 30°), and 1.5 times with a 90° instruction.
Brass olives on copper tube
In plumbing and heating, a compression fitting usually means a brass fitting with a soft olive on copper tube; the olive is also sold as a compression sleeve. In Europe these fittings are standardised in EN 1254-2:2021 12. The ring does not cut; it is pressed around the tube as the nut is tightened.
Soft copper tube needs a support sleeve in its end, otherwise the tube gives way 4, 6. Do not wrap the ring or the nut thread with hemp or tape: the seal is made at the ring 6, 10. A wheel cutter is fine for copper here; the rule to saw applies to bite-type rings on steel tube.
How far a brass olive is tightened is stated in its manufacturer’s instructions. The figures for steel bite-type rings do not apply. For gas lines, follow your local codes and use fittings approved for gas.
Common mistakes and fixes
| Symptom | Cause | Fix |
|---|---|---|
| Leaks on the pressure test | too little travel on initial make-up, no collar | remake as specified or pre-assemble again |
| Tube pulls out | tube not at the shoulder or ring fitted the wrong way round | check the ring (cutting edge towards the tube end), remake |
| Ring moves axially | not tightened enough | remake as specified |
| Cone damaged, nut runs hard | over-tightened or not oiled | replace the parts |
| Leak on stainless | steel ring on stainless tube, or pre-assembly in the fitting body instead of a hardened tool | stainless ring, pre-assemble in a hardened body 3, 6 |
| Ring bites unevenly | crooked cut, burr | saw the tube square and deburr 3, 4, 6 |
| Leak under pressure | attempt to tighten under pressure | never tighten under pressure, it is a danger to life. Depressurise the line 3 |
Reuse
A bite-type fitting can be taken apart and made up again. Tube, ring and body then belong together. A fitting body used for direct pre-assembly is used for that only once 4.
On re-make-up, the final make-up rule applies: up to the noticeable torque rise, then 30° to 90°, stainless up to 180° 3, 4, 6. Replace soft seals, for example on the stud end.
You cannot get the ring off the tube any more; it has bitten in. To reconnect the line, saw off the tube end with the ring or use a ring puller.
Good to know: myth and fact
The ring does not bite in and the tube can slide out under pressure. Result: a leak or a blown-off line.
Under-tightened: the gap gauge still enters the gap, and the joint leaks on the pressure test.
A necked-in tube end and burrs make the ring bite unevenly and keep the tube off the shoulder. Result: leaks and a shorter service life.
Over-tightening crushes ring and cone, and the fitting cannot be made up again. Tightening under pressure is a danger to life.
Matching products
Bite-type fittingCutting Ring Fitting 6mmView product →
CategoryPneumatic ConnectorsView category →
CategoryPiping & Pipe ConnectorsView category →
Push-in fittingPush-in Elbow Fitting M5View product →Frequently asked questions
How many turns does a compression fitting need?
A two-ferrule fitting up to 1 in (25 mm) needs 1¼ turns from finger-tight, small sizes (2–4 mm, 1/16–3/16 in) ¾ turn 8. A DIN bite-type fitting usually needs 1¼–1½ turns from first contact, Schwer 1–1¼ 3, 4, 6, 7. For brass olives on copper, follow the manufacturer’s instructions.
Do I use Teflon tape on compression fittings?
Not on the ferrule or cone: the seal is made at the ring itself, and manufacturers specify oil or grease, not a sealant 6, 10. How the stud thread of the body is sealed depends on its design and is stated in the data sheet. Thread types are listed in our thread chart.
Can compression rings be reused?
Yes, but tube, ring and body then belong together. On re-make-up, tighten only to the noticeable torque rise and then 30–90° (stainless up to 180°), never the full initial make-up again 3, 4, 6. Two-ferrule fittings: back to the previous position, then tighten slightly 10.
How do I get a compression fitting off?
The nut comes off, but the ring stays on the tube. To reconnect, saw off the tube end with the ring or pull the ring off with a ring puller.
Compression fitting or push-to-connect?
In industry, push-in fittings are meant for pneumatics and low pressure. Where steel or stainless tube runs at higher pressure, bite-type or compression fittings are used.
Sources
- DIN EN ISO 8434-1:2018-11, Metallic tube connections for fluid power and general use – Part 1: 24° cone connectors; replaces DIN EN ISO 8434-1:2008-02 (title and edition per DIN Media).
- DIN 2353:2013-01, Solderless compression couplings with cutting ring – complete couplings and overview (status current per DIN Media); plus Parker Hannifin: DIN-ISO-EO comparison 4091-2/DE, 04/2007, p. 3.
- Parker Hannifin: assembly instructions for DIN fittings 4015/DE, 08/2005, pp. 2–10; current edition AI/4015-2/DE, 04/2019, p. 17 “new EO assembly instruction for 30° final make-up”.
- VOSS Fluid: assembly instructions 2S tube fittings (undated).
- VOSS Fluid: assembly instructions VOSS Ring M (undated).
- HANSA-FLEX: technical information – assembly instructions cutting ring/tube fitting, 03/2024.
- Schwer Fittings: assembly instructions for bite-type fittings to EN ISO 8434-1 (undated).
- Swagelok: An Installer’s Pocket Guide for Tube Fittings, MS-13-58, 1998.
- Swagelok: Instructions for Swagelok Jacketed Tube Connector, MS-CRD-0202, 10/2012 (gap inspection gauge).
- Swagelok: Tube Fitting Instructions for 1 in. (25 mm) and Smaller Fittings, MS-12-01, Rev. F, 03/2021.
- HANSA-FLEX: product data for union nuts to ISO 8434-1/DIN 3870, series LL, L and S (thread, tube outside diameter, pressure rating), retrieved 2026-11-02.
- DIN EN 1254-2:2021-10, Copper and copper alloys – Plumbing fittings – Part 2: Compression fittings for use with copper tubes; replaces DIN EN 1254-2:1998-03 (per DIN Media).
- shukchok: own analysis of 10 make-up instructions from 5 manufacturer documents (sources 3 to 10) and own calculation of the axial travel s = (φ / 360°) · P for 19 sizes, 2026-11-02.
How to cite this page
Scharff, A. (2026): Compression and bite-type fittings: how many turns, how to check, what goes wrong. shukchok.com, Updated 12 November 2026. https://shukchok.com/en-ae/wissen/schneidringverschraubung