Compression fittings to DIN 2353 and ISO 8434‑1, 4 mm to 42 mm

No — not as a union. 800 bar is the published ceiling of the S series across every body style, and on the straight union the bands are PN 630 at 6 to 14 mm, PN 400 at 16 to 30 mm and PN 315 at 38 mm. So an S‑series 30 mm union is a 400 bar part and a 38 mm one is 315 bar — the same as an L‑series 6 mm. Design to the size and the body style, never to the series letter, and ask us to confirm the figure for the exact part.

Wall thickness of the fitting and therefore pressure. LL is extra light, to 100 bar, and only exists from 4 to 12 mm. L is light, to 500 bar at the top of the range, covering 6 to 42 mm. S is heavy, to 800 bar, covering 6 to 38 mm. They also have different nut threads at the same tube size, which is what stops you fitting the wrong one by accident — and what makes the nut thread so useful for identification.

No. 6 mm exists in all three series but the parts are different: the nut is M10×1.0 in LL, M12×1.5 in L and M14×1.5 in S. Same tube, three incompatible fittings at three pressure classes. This is exactly why a size on its own is never enough to order from — we need the size and the series, or the pressure so we can pick it.

On stainless: nothing up to +20 °C, then 4% to +50 °C, 11% at +100, 20% at +200, 29% at +300 and 33% at +400 °C. On brass a flat 35% across its whole range. On steel, no reduction — but its ceiling is only +120 °C. Take the percentage off the size rating, not the series ceiling.

Treat it as no. A ring that has bitten has cut a groove and work‑hardened; put it on a fresh tube and it will not raise a proper collar. A joint can be broken and remade a limited number of times with the same ring back onto the same tube in the same position, which is what service work relies on. Anything else — new tube, new position, ring swapped between joints — needs a new ring. They are the cheapest part of the assembly.

Back the nut off after pre‑assembly and look at the tube. There must be a visible collar of material standing ahead of the ring, right the way round. That collar is the joint. If it is missing, or only on one side, the nut was not turned far enough or the tube was not square and held to the abutment — and no amount of extra torque at final make‑up will fix it.

For a handful of joints, no — the fitting body itself can be used. For any volume, yes, and it pays for itself quickly. It forms the collar to the same depth every time, lets you make rings up on the bench rather than in an awkward corner of the machine, and it saves the fitting body: pre‑assembling in the body wears the 24° cone that then has to seal.

Because turning the body drags the cone round against the ring, which spins the ring on the tube and wipes out the bite it has just cut. You get a joint that feels tight and leaks under pressure, and a ring with a bright rubbed band on it. Two spanners, every time: one holding the body, one on the nut.

Steel for ordinary hydraulic oil duty — no pressure derating and the lowest cost, but limited to +120 °C. Stainless where there is corrosion, washdown, or temperature above that — it reaches +400 °C, at a pressure cost. Brass for low pressure and compatible media only, remembering the flat 35% reduction. Tell us the fluid and the environment and we will choose it with you.

Generally yes — that is the point of the standard. The 24° cone, the nut threads and the tube sizes are defined by DIN 2353 and ISO 8434‑1, so a body from one maker takes a nut and ring from another of the same size and series. In practice we still recommend keeping ring and body from the same source on a critical joint: the tolerances are shared but the ring geometry and hardness are where makers differ.

The range is designed for commercial hydraulic oils. Water glycol, phosphate ester, fuel, compressed air, gas or anything chemical is a material question, not a pressure one — the fitting may be fine and the seal, or the brass, may not. Tell us the medium, the concentration and the temperature, and we will confirm the material before you order rather than after.

More than people expect, and it is the commonest reason a joint that was assembled correctly still leaks. Three things matter. Outside diameter tolerance — the ring is cutting to a designed depth, so a tube on the low limit gives a shallow bite and one on the high limit over‑stresses the ring. Wall thickness — too thin for the series and the tube waists or collapses instead of taking the bite; this is what decides whether you are in LL, L or S as much as the pressure does. Hardness — a tube harder than the ring will not let the ring bite at all, and a very soft one lets it cut too deep. Cold‑drawn seamless hydraulic tube to a recognised tolerance standard is what the fittings are designed around. Send us the tube specification you are buying and we will check it against the fittings before you commit — a mismatch here is invisible until the system is up to pressure.

Only if it is then squared and deburred properly. A hacksaw leaves the end out of square and burred inside and out: the out‑of‑square end stops the tube seating on the abutment so the collar forms unevenly, and the internal burr breaks off into the system later. Square it, deburr both sides, clean the swarf out — then fit.