Materials & Manufacturing.

A cast body and a machined body can leave the polishing shop looking identical. The difference is what sits under the surface, and whether you can prove where the metal came from.

Why bar stock

Metal shrinks as it solidifies. In a casting that shrinkage has to come from somewhere, and where the section is thick or the feeding imperfect it comes from voids left inside the wall.

None of that matters while the void stays buried. The problem is that a hygienic bore does not stay buried: it is polished, often electropolished, and both remove material. Remove enough and a subsurface void becomes a surface pit, in the wetted bore, after finishing, where cleaning cannot reliably reach it.

Wrought bar has been mechanically worked after solidification. There are no shrinkage voids to expose. What you machine is what you get.

Bar stock vs castings covers the trade-off honestly, including where a casting is the right engineering answer.

What the paper trail proves

Stainless is melted in batches. Each batch is a heat, and its heat number ties finished metal back to the mill's record of that melt: chemistry and mechanical properties measured on that specific batch.

One certificate is rarely the whole story. A finished assembly is a stack of them.

• The body carries the heat number of the bar it was cut from.
• Every component welded to it carries its own certificate: hose barb, ferrule, tube.
• The filler rod carries one too, which is the one people forget.
• The weld map records which joint was made where, so the stack can be read back joint by joint.

The document that carries the body is a Material Test Report, typically to EN 10204 3.1: issued by the manufacturer's own authorised inspection representative, reporting results from the product actually supplied rather than a similar batch. It ships with every Aquasyn order as standard, not on request.

Surface finish, and why the method matters

Two different things get called the finish. Ra is a measurement, the arithmetic average roughness. The SFV designation is a grade that bundles a roughness limit with how the finish was produced.

The distinction matters because two surfaces at the same Ra are not equivalent if one was mechanically polished and the other electropolished. Mechanical polishing cuts and smears, leaving a worked layer that drags material over micro-defects. Electropolishing removes material preferentially from high points, taking that smeared layer away rather than covering it.

If a specification says SFV4 and a quote says 15 Ra without saying electropolished, those are not yet the same thing.

Size can remove the question entirely. A ⅛″ bore cannot be polished at all, because there is no way to get a tool into it, so no Ra value and no SFV grade apply. From ¼″ through 4″ the full range is available.

The route through the shop

Finishing is not one step, and the sequence is not a straight line. Outside diameter, then bore, then outside again, because welding and internal work both disturb the exterior. Two stages are conditional: a part already on the shelf skips machining, and electropolishing happens only where the specification calls for it.

The full route, stage by stage, is on the capabilities page.

Beyond 316L, bodies are available in Hastelloy C, AL6XN and Titanium where the chemistry needs them.