The short answer
On turned-shaft RFQs, a **wrench flat** is not the same as a [keyway](https://3dwk.com/resources/keyway-callouts-on-cnc-turned-shafts), a [knurl](https://3dwk.com/resources/knurling-on-cnc-turned-shafts), or a general “mill two sides.” A wrench flat is a milled chord (or a pair of parallel chords) cut on a turned diameter so a wrench, a clamp, or an anti-rotation face has a known width across flats. Silence on that width, on flat length, on which diameter is cut, and on whether the flat may break a shoulder, bearing journal, or thread, is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the extra minutes of a simple side mill alone.
This guide is for buyers packaging turned RFQs where a hex, a double-flat, or a single anti-rotation face is sketched on a shaft with no width or keep-out. Illustrations use an **Example part** only—not a customer shaft. Sibling notes live in the [turned stainless shaft drawing guide](https://3dwk.com/resources/turned-stainless-shaft-drawing-guide) and [milled and turned features on one CNC part](https://3dwk.com/resources/milled-and-turned-features-on-one-cnc-part); here we focus on **wrench-flat packaging** so estimators do not have to guess whether a “standard hex” is 16 mm across flats on Ø20, and whether it may nick shoulder A.
What wrench flats mean for quoting
A **wrench-flat pack** names the width across flats (or the residual height of a single flat), the axial length of the flat, the parent diameter, and keep-outs from adjacent shoulders, threads, or journals. It is not a keyway width, and a general “add hex for assembly” cloud does not tell the shop the cutter path or the remaining chord. Process pages for stainless turning and milling ([CNC turning SS 316 robotics](https://3dwk.com/en/cnc-turning/ss-316/robotics.html), [CNC turning SS 316](https://3dwk.com/en/cnc-turning/ss-316.html), [CNC 3-axis SS 316](https://3dwk.com/en/cnc-3axis/ss-316.html)) assume flats are dimensioned when lots mix assembly pads with bearing diameters on the same blank.
Do not bury “hex as needed” inside a notes cloud. Put **TWO FLATS, 16 ACROSS, LENGTH 12, ON Ø20, START 4 FROM SHOULDER A, DO NOT BREAK JOURNAL B OR M12 THREAD** on the PDF and mirror it in RFQ text. Background: [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote), [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote), [shoulder fillet versus undercut](https://3dwk.com/resources/shoulder-fillet-vs-undercut-cnc-turned-shafts).
Width across flats, length, and parent diameter
Name the width across flats, not only “hex.” A 16 mm pair of flats on Ø20 is a different stock removal than a 13 mm pair, and a single anti-rotation flat is a different setup from a two-flat or three-flat pattern. Show the axial start and end so the mill does not wander into a [thread relief](https://3dwk.com/resources/thread-relief-runout-notes-cnc-turned-parts) or a retaining feature. If the flat is only for a fixture during assembly, say so—cosmetic blending can then stay looser than a wrench pad that must accept a 16 mm open end.
Stainless 316 bar $/kg planning bands sit in the mid-commodity stainless range under **rates.v1.1** material tables; material cost is rarely the flat story—second-op milling, orientation to a keyway or thread start, and journal keep-outs are.
Keep-outs, blends, and mill-turn versus second op
Say whether a small blend or a sharp wall is required at the ends of the flat, and whether the flats must be clocked to a keyway, a hole, or a thread start. A mill-turn cell can often cut flats in the same chucking; a plain turned blank that needs a second milling setup should not be hidden behind “hex standard.” [Concentricity versus runout](https://3dwk.com/resources/concentricity-vs-runout-callouts-cnc-shafts) on the parent diameter stays a separate geometry note—the flats do not replace it.
Tolerance and inspection traps
Calling “standard hex on the shaft,” mixing a tight width-across-flats tolerance with an unspoken parent-diameter change, or asking for 100% optical photos of every blend, all force **needs_manual**. Default non-critical assembly flats to a written width and length, and put a tight tolerance only where a wrench or a mating notch must fit. Related: [ISO 2768 general tolerances on CNC RFQs](https://3dwk.com/resources/iso-2768-general-tolerances-cnc-rfq), [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
Illustration 1 shows an **Example part** shaft with a labeled two-flat pack on Ø20 versus a short anti-rotation single flat that must not break journal B.
Example part walkthrough
**Example part:** Stainless 316 turned shaft ~Ø20 × 80 mm, two wrench flats 16 mm across × 12 mm long on the Ø20 diameter, starting 4 mm from shoulder A, keep-out on journal B and on the M12 thread, ISO 2768-m general. With STEP + **2 FLATS 16 ACROSS × L12 ON Ø20; START 4 FROM A; DO NOT BREAK JOURNAL B / M12**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “add hex for wrench” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“standard hex as needed”) versus a labeled width-length-keep-out pack and the clearer estimate path.
What widens bands fastest
Unlabeled “hex,” flats that collide with a thread or a bearing seat, width given without the parent diameter, and 100% cosmetic inspection of every mill blend. Quantity breaks help unit minutes but do not erase flat-pack ambiguity—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [how workholding changes a CNC quote](https://3dwk.com/resources/how-workholding-changes-cnc-quote).
What to do next
Mark each wrench or anti-rotation flat with a **width, length, parent diameter, and keep-out**, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [CNC machining](https://3dwk.com/cnc-machining-service.php), [materials](https://3dwk.com/materials.php). Treat **rates.v1.1** min/mid/max as estimates, not invoices. If the UI shows **needs_manual**, answer the flat questions rather than forcing a fake price.
Common questions
Is a wrench flat the same as a keyway?
No. A keyway is a slot that carries torque through a key. A wrench flat is a milled chord for a tool or a clamp. If you need both, dimension both and show the clocking between them.
Can the flats break into a shoulder or a thread runout?
Only if you write that they may. A flat that nicks a bearing journal or a full-form thread is usually a reject. Put a keep-out, or move the flat to a dedicated diameter.
Do I need a tight tolerance on width across flats?
Only when a specific wrench, a mating notch, or a location fixture depends on it. Many assembly pads work to a general tolerance if the width and length are named. Tight width plus a tight parent diameter should be a conscious stack, not a default.
How should I call out a single anti-rotation flat?
Name the residual height or the depth of cut from the parent diameter, the length, and the clocking to any hole or keyway. “One flat for assembly” without a depth leaves the chord—and the quote band—open.