Buying Hydraulic Cylinder Tube and Piston Rod from Taiwan: The Spec Language That Gets You Quoted

All three are ways of turning a rough seamless or welded tube into a bore a piston seal can survive in, and they get there differently. Honing is abrasive: rotating stones cut the bore to size and leave a cross-hatch pattern that holds a film of oil. Skiving is a single-point cutting pass that shaves the bore round and straight at high removal rate; roller burnishing follows immediately behind it in the same machine, cold-working the surface with hardened rollers so it is smoothed and work-hardened rather than abraded. The industry shorthand "SRB tube" means skived-and-roller-burnished, and it is a two-step combination, not an alternative name for honing.

The practical difference is economics and size, not a quality hierarchy. Honing removes little material, so it starts from a tube already close to size and is the usual route on small and medium bores. Skiving removes a lot in one pass, so it tolerates a rougher starting tube and scales to large diameters where honing time would be punitive. A burnished surface is also work-hardened, which some designers value for seal life; a honed cross-hatch is valued for oil retention. Both are normal in production cylinders.

A third option is cheaper than either: unhoned tube with the outside diameter hard-chrome plated and ground. That is not a cylinder barrel — it is stock for the parts of an assembly where the outside surface is the working surface, and its bore is left loose. Buying it by mistake because the price looked good is the most common error in this segment.

Name an ISO tolerance grade for the bore, not a millimetre band, because a grade scales with diameter and a fixed band does not. The published tables in this segment quote H7, H8 and H9 for finished bores, and the actual numbers follow the standard: on a 15 mm bore, H7 is +0.018/-0 mm, H8 is +0.027/-0 and H9 is +0.043/-0; on a 120 mm bore, the same three grades open out to +0.035, +0.054 and +0.087. That is the entire point of specifying a grade — H8 means something different at 20 mm and at 200 mm, and it means it consistently.

For roughness, name Ra and a band. Finished hydraulic bores in this segment are typically quoted around Ra 0.2–0.8 µm for honed surfaces and Ra 0.4–0.8 µm for skived-and-burnished ones. Some Japanese-convention tables still use the older JIS grade notation (for example 0.8S–3.2S) rather than Ra; if your drawing and the mill's table use different conventions, resolve it in writing before the order rather than at inspection.

Straightness is the spec buyers forget, and it is the one that scraps long tubes. The common published figure in this segment is 1/1000 — one millimetre of deviation per metre of length — or better, quoted against a JIS reference. On a 6-metre tube that is 6 mm, which may or may not be acceptable to your machining operation. If it is not, say so at enquiry stage; straighter than the mill's standard is a process decision, not a sorting decision.

Hard chrome on rod is specified by three numbers together: plating thickness, surface hardness, and the diameter tolerance after plating. The tables we have indexed quote roughly 20 µm ±5 of chrome as the common thickness (15 µm ±5 on some induction-hardened grades), surface hardness in the region of HV 800 and above, and a finished diameter tolerance of f7 or f8. Any one of those three alone is not a specification. Thickness without hardness allows soft chrome; hardness without a tolerance allows a rod your seal will not accept.

Underneath the plating, the substrate choice is the real engineering decision. Medium-carbon steel is the commodity base; a chrome-moly alloy grade raises core strength for high side-load duty; an induction-hardened rod adds a hard case (surface hardness quoted around HRC 54 ±2 on the carbon grade and HRC 62 ±2 on a bearing-steel bar in the tables we hold) so the rod resists denting from grit before the chrome cracks. Stainless rod exists and is chrome-plated too — the stainless is for the corrosion of the substrate if the plating is breached, not a substitute for plating.

Two honest caveats about chrome. First, it is not a corrosion coating in the marine sense: hard chrome is micro-cracked by nature, and in salt or outdoor service the durable answer is a thicker or duplex system (nickel under chrome), or a thermally sprayed coating such as HVOF tungsten carbide, or a ceramic-coated rod. Those alternatives are widely available globally but are a much thinner specialism in Taiwan's cylinder-component cluster than plain hard chrome — do not assume a mill quoting chrome rod can quote HVOF. Second, hard chrome plating uses hexavalent chromium baths, which are subject to authorisation under EU REACH; the status of specific uses changes, so if you are importing into the EU, confirm the current position with your own regulatory adviser rather than with the plating shop.

The pairing is not arbitrary, and the mills publish it. The tables we hold list a recommended rod diameter for each bore, split by service: a pneumatic cylinder uses a much thinner rod than a hydraulic one at the same bore, because the rod is sized for buckling and for the area ratio, not for the bore. Three illustrative rows from those published pairing tables:

Rated pressure moves with wall thickness, so the wall is a pressure decision before it is a cost decision. In one indexed table, a 15 mm bore at 21 mm OD is rated 416 kg/cm² while a 120 mm bore at 135 mm OD — the same 3 mm wall arithmetic does not apply, but the same nominal jump in size — is rated 130 kg/cm². If you send a bore and a length without a wall or a working pressure, the mill will pick a wall, and it will be their standard, not yours.

Material is usually a Japanese-convention designation in this segment. The overwhelming majority of the tube lines we have indexed are a mechanical-tube grade in the JIS STKM family; rod lines are mostly a medium-carbon grade with alloy, bearing-steel and stainless variants alongside, and a minority of aluminium-alloy tube appears for pneumatic and light-duty work. European buyers used to the DIN equivalents should ask for the cross-reference in writing rather than assuming it.

What the mill is not doing is designing your cylinder. Seal selection, port and mounting design, cushioning, rod-end thread and stroke calculation sit with you or with a cylinder builder. The mills in this segment sell metres of qualified tube and bar, cut, finished and certified — which is exactly why the enquiry has to be dimensional.

The limits are specific. Very large bores — above the ~350 mm skiving ceiling visible in the tables we have indexed — push you toward mills in Korea, Japan, China or Europe that are set up for heavy sections. Chrome-free rod technologies (HVOF, ceramic, nitrided-and-polished) are a thin specialism here. So is anything requiring pressure-vessel-grade documentation regimes, radiographic inspection of the tube, or a material certificate under a European pressure directive — ask before assuming, because a mill that cannot issue the paperwork will still happily make the part.

And at the small end, a one-off need for two metres of honed tube is not an import project. Freight, minimum cut charges and the handling of a bent 6-metre bar will beat the unit-price saving comfortably. Buy that from a stockist in your own country; source from Taiwan when you are buying repeating sizes in quantity or building a cylinder line.

Write the four numbers first — bore, wall, tolerance grade, roughness band — then the length and the certification, then go looking for a mill. An enquiry written in the language above lands on the desk of someone who can price it without a meeting, and it is the single biggest determinant of how fast you get a real number back.

For transparency about what Taiwan Supplier Hub brings to this specific segment: the hydraulic tube and rod catalogue we hold is genuinely first-hand and genuinely narrow — 763 indexed line items as of 11 September 2026, all of them cylinder tube and piston rod, drawn from a small number of specialist mills rather than a broad survey of the island. The wider hardware file behind it is 464 Taiwan supplier records — 214 researched one at a time from the manufacturer's own website, and 250 open-registry leads that are named and located but not individually verified — and most of them do stamping, forging and fastener work rather than tube. If you tell us the bore, the tolerance and the annual metres on our request page, we will take that to mills that can quote it, and say plainly if the size you need sits outside what this cluster does.