The short answer
On CNC brackets, **perpendicularity** of a tab or flange to a named datum face is not the same control as **flatness** of that face, and it is not **parallelism** of two opposite pads. Perpendicularity asks how square one surface (or an axis) is to a datum; the datum must be named, and the tolerance applies to that relationship only. Silence on **which tab is controlled**, **which face is datum A**, and **whether “90° / square” was meant as GD&T** is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the pocketing minutes alone.
This guide is for buyers packaging stainless brackets where a notes cloud says “tabs 90°” or “square to base” next to hole patterns. Illustrations use an **Example part** only—not a customer medical device. Sibling notes live in [flatness, parallelism and perpendicularity on machined parts](https://3dwk.com/resources/flatness-parallelism-perpendicularity-machined-parts), [flatness vs parallelism callouts on CNC plates](https://3dwk.com/resources/flatness-vs-parallelism-callouts-cnc-plates) and [position vs profile tolerances on CNC brackets](https://3dwk.com/resources/position-vs-profile-tolerances-cnc-brackets); here we focus on **perpendicularity callouts on bracket tabs** so estimators do not treat every face as a 0.02 mm all-over square requirement.
What perpendicularity means for quoting
A perpendicularity control on a tab says the tab face (or the tab’s mid-plane, if you say so) must lie within a tolerance zone square to datum A—usually the mounting face that bolts to the customer structure. It does not automatically control hole position on that tab, and it does not flatten datum A. Shops plan whether the tab can be finished in the same setup as A or needs a second operation, and whether a CMM, a granite square or a simple indicator sweep is the inspection intent. Process pages for medical stainless ([CNC 3-axis SS 316 medical](https://3dwk.com/en/cnc-3axis/ss-316/medical.html), [CNC 5-axis SS 316 medical](https://3dwk.com/en/cnc-5axis/ss-316/medical.html), [CNC turning SS 316 medical](https://3dwk.com/en/cnc-turning/ss-316/medical.html)) assume those notes when lots mix simple plates with bent-looking CNC tabs.
Do not write “90° tab / square as CAD.” Put **DATUM A = MOUNTING FACE; TAB FACE B PERPENDICULAR TO A WITHIN 0.05** on the PDF and mirror it in RFQ text. Background: [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts), [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands), [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote).
Datums, tabs and what not to substitute
Name datum A as a real, inspectable face—not “the long direction of the part.” If two tabs must both be square to A, control each (or control a pattern) rather than hoping one note covers every wall. Do not replace perpendicularity with a title-block angularity of 90°±0.5° unless that looser note is truly what you want; an angle dimension without a datum is easier to misread across setups. Hole position on the tab remains a position or profile control to the same datum reference frame—mixing “holes must be square” into the perpendicularity note hides which feature is being inspected.
Stainless 316 bar/plate planning bands sit above commodity aluminum under **rates.v1.1** material tables ([stainless 304 vs 316 vs 17-4PH](https://3dwk.com/resources/stainless-304-vs-316-vs-17-4ph)); material cost is rarely the square-up story—second setups, thin-tab spring and CMM minutes are.
When a looser square note is enough
If the tab only clears a cover or carries a cable clamp, an ISO 2768 angular default or a generous perpendicularity (stated as such) is enough. Reserve a tight 0.02–0.05 mm style control for tabs that pick up a sealing face, an optical rail, or a mating connector. Applying the tight number to every wall of a milling blank treated like a bent sheet-metal bracket is how quotes jump to **needs_manual**.
Tolerance and inspection traps
Calling “all faces square 0.02,” omitting datum A, stacking flatness on A + perpendicularity on B + parallelism on C with no setup story, or requiring 100% CMM of every non-functional rib as if it were tab B, all force **needs_manual**. Related: [CMM sampling plans for CNC lots](https://3dwk.com/resources/cmm-sampling-plans-for-cnc-lots), [ISO 2768 general tolerances on CNC RFQs](https://3dwk.com/resources/iso-2768-general-tolerances-cnc-rfq). Thin tabs spring after release from the vise; if you need the control in the free state, say so.
Illustration 1 shows an **Example part** bracket with labeled perpendicularity of the tab to datum A, separate from flatness of A and from hole position.
Example part walkthrough
**Example part:** Stainless steel 316 bracket ~70×40×8 mm envelope, mounting face A, one 90° tab ~25 mm tall, two through holes in the tab, ISO 2768-m general. With STEP + **DATUM A = MOUNTING FACE (FLATNESS NAMED SEPARATELY IF NEEDED); TAB FACE B ⊥ A 0.05; HOLE POSITION TO A/B SEPARATE**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “all tabs square, 90° as modeled” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“90° / square”) versus a labeled datum-and-perpendicularity pack and the clearer estimate path.
What widens bands fastest
All-over square notes with no datum, tight perpendicularity on every rib, inspection method left implicit on a thin springy tab, and hole position hidden inside the square-up note. Quantity breaks help unit minutes but do not erase datum 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
Name **datum A**, apply **perpendicularity only to the functional tab**, keep hole position separate, 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 datum-and-square questions rather than forcing a fake firm price.
Common questions
Is perpendicularity tighter (and costlier) than writing 90°±1°?
A small GD&T zone referenced to a datum is a different requirement than a loose angle dimension. Under **rates.v1.1** estimates, the tighter, datumed control usually needs a clearer setup and inspection plan. Use the control that matches function.
Can I use parallelism instead if the tab has an opposite face?
Parallelism relates two features that should stay parallel. A single tab standing on a base is a perpendicularity story. See [flatness vs parallelism callouts on CNC plates](https://3dwk.com/resources/flatness-vs-parallelism-callouts-cnc-plates) when the features really are opposite faces.
Does the mounting-face flatness come “for free” with perpendicularity?
No. Flatten datum A with its own callout if the mount must seal or sit without rock. Perpendicularity assumes that datum; it does not invent a flatness value.
How should I inspect a thin tab?
Say whether the part is checked in a free state or clamped as assembled. Thin stainless tabs can spring; a CMM plan that ignores that often disagrees with a square on the bench. See [CMM sampling plans for CNC lots](https://3dwk.com/resources/cmm-sampling-plans-for-cnc-lots).