The short answer
On shaft RFQs, **circularity** (roundness) and **cylindricity** are not interchangeable form notes. Circularity controls a **2D cross-section**—each circular element must lie between two coplanar concentric circles. Cylindricity controls the **3D cylindrical feature**—the entire surface must lie between two coaxial cylinders, so taper, banana bow, and local roundness are all in the same tolerance. Silence on which symbol applies, on the datum (if any), and on whether you actually meant **runout** or **concentricity**, is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the turning minutes alone.
This guide is for buyers packaging stainless shaft RFQs where CAD shows a Ø12 h6 journal with a generic “round and straight” note, or a title-block cloud that mixes circularity with runout. Illustrations use an **Example part** only—not a customer automation roller. Sibling notes live in [concentricity vs runout callouts on CNC shafts](https://3dwk.com/resources/concentricity-vs-runout-callouts-cnc-shafts) and [flatness, parallelism and perpendicularity on machined parts](https://3dwk.com/resources/flatness-parallelism-perpendicularity-machined-parts); here we focus on **form packaging** so estimators do not guess a full-length cylindricity inspect on a relief that only needed a local roundness check.
What each form control means for quoting
**Circularity** is inspected in cross-sections, typically on a roundness checker or CMM circles. It does not, by itself, control axis straightness or taper along the length. **Cylindricity** is a compound form: it is more demanding to machine and to report because the whole journal (or the named length) must stay inside a cylindrical tolerance zone. **Runout** and **concentricity** relate one feature to a datum axis; they are not substitutes for a form-only circularity note. Process pages for stainless turning and automation-adjacent shafts ([CNC turning SS 316](https://3dwk.com/en/cnc-turning/ss-316.html), [CNC turning SS 316 robotics](https://3dwk.com/en/cnc-turning/ss-316/robotics.html), [CNC 3-axis SS 316 robotics](https://3dwk.com/en/cnc-3axis/ss-316/robotics.html)) assume form notes when lots mix open turned diameters with tight journals.
Do not bury “must be round” inside a notes cloud. Put **CIRCULARITY 0.01 ON JOURNAL Ø12 OVER THE 18 MM LAND** or **CYLINDRICITY 0.02 ON Ø12 BETWEEN FACES C–D** on the PDF and mirror it in RFQ text. Background: [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands), [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts).
When circularity is enough
Use a named circularity when each station of the journal must be round but a small taper or bow is already controlled by a size tolerance, a runout to a datum, or a later grind. Use cylindricity when the functional fit is a long bearing land that cannot accept taper or banana even if every slice is round. Calling cylindricity 0.005 on a 80 mm as-turned 316 shaft, without a grind allowance or a shorter inspected land, often forces **needs_manual**. Related process and inspection notes: [ISO 2768 general tolerances on CNC RFQs](https://3dwk.com/resources/iso-2768-general-tolerances-cnc-rfq), [surface roughness Ra callouts that raise quotes](https://3dwk.com/resources/surface-roughness-ra-callouts-that-raise-quotes), [position vs profile tolerances on CNC brackets](https://3dwk.com/resources/position-vs-profile-tolerances-cnc-brackets).
Stainless 316 bar $/kg planning bands sit above commodity aluminum under **rates.v1.1** material tables; material cost is rarely the form story—inspect method, grind stock, and whether cylindricity applies to the full length are.
Cylindricity, taper and the inspected length
State the axial extent. “Cylindricity on Ø12” without “between C and D” or “over the 18 mm land” lets the inspector include undercuts, thread runout, or a wrench hex. For most shaft buyers, a **short circularity on the bearing land** plus a size/runout pack is clearer than one tight cylindricity on the entire turned outline. If a later centerless grind is planned, say the stock and which form applies before versus after grind.
Tolerance and inspection traps
Mixing circularity with a cylindricity symbol on the same diameter, applying 0.005 cylindricity to a long as-turned bar with no grind, asking for 100% CMM cylindricity on every relief, or writing “round and concentric” without a datum or a form choice, all force **needs_manual**. Default non-critical diameters to ISO 2768-m and put form only on the journals that carry load. Related: [perpendicularity callouts on CNC brackets](https://3dwk.com/resources/perpendicularity-callouts-cnc-brackets), [flatness vs parallelism callouts on CNC plates](https://3dwk.com/resources/flatness-vs-parallelism-callouts-cnc-plates). The inspect method (roundness checker vs CMM vs runout stand) belongs next to the form note when it is contractual.
Illustration 1 shows an **Example part** shaft with labeled circularity on a short journal versus cylindricity over a longer land on the same diameter family.
Example part walkthrough
**Example part:** Stainless Steel 316 turned shaft ~Ø16 × 90 mm, one Ø12 h6 journal 18 mm long, a relief, and a Ø10 bearing land 28 mm long, ISO 2768-m general. With STEP + **Ø12 LAND: CIRCULARITY 0.01; Ø10 LAND: CYLINDRICITY 0.02 BETWEEN C–D; RUNOUT 0.03 TO DATUM A (CENTERS)**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “all diameters round and cylindrical as needed” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“must be round”) versus a labeled form-callout pack and the clearer estimate path.
What widens bands fastest
Unlabeled mix of circularity and cylindricity, full-length cylindricity on as-turned 316 with no grind stock, missing inspect length, and 100% reports on every relief. Quantity breaks help unit minutes but do not erase form-callout ambiguity—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
What to do next
Mark each functional journal as **circularity** or **cylindricity**, name the inspected length and any grind stock, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [CNC machining](https://3dwk.com/cnc-machining-service.php), [quality](https://3dwk.com/quality.php). Treat **rates.v1.1** min/mid/max as estimates, not invoices. If the UI shows **needs_manual**, answer the form-callout questions rather than forcing a fake firm price.
Common questions
Is cylindricity always tighter than circularity?
Not automatically under **rates.v1.1** estimates. A loose cylindricity can be easier than a very tight circularity plus a separate straightness. The wider band usually comes from applying cylindricity to a long as-turned length without saying so.
Can I use runout instead of cylindricity?
Runout includes datum relationship and can catch some form error, but it is not a drop-in replacement. If you only care that each slice is round, circularity is the clearer note; if you care about taper along a land, name cylindricity or a size + taper rule.
When is circularity on one station enough?
When the land is short, size already limits taper, or a later grind will establish the 3D form. Write which condition applies so the as-turned operation is not over-inspected.
How should I call out finish with form?
Put Ra next to the same journal as the form note. A tight cylindricity with a rough as-turned Ra is a conflicting pack and often returns **needs_manual**.