The short answer
A **slotted hole** on a CNC plate is not a round hole that “can be a bit long,” and it is not a license to leave fastener position silent. A usable slot callout names the **width**, the **length** (end-to-end or a width plus a center-to-center), the **end-radius** (full stadium ends versus a boxed slot), the **orientation**, and which of those dimensions actually locates the fastener. Silence on which axis is clearance and which axis is a fit is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the extra minutes of a slotting pass alone.
This guide is for buyers packaging milled plates where adjustment slots, thermal-growth slots, or oversized fastener slots are modeled as skinny pockets or labeled only “slot for M6.” Illustrations use an **Example part** only—not a customer panel. Sibling notes live in [minimum hole-to-edge distance on CNC plates](https://3dwk.com/resources/minimum-hole-to-edge-distance-dfm-cnc-plates) and [dowel-pin hole location](https://3dwk.com/resources/dowel-pin-hole-location-dfm-cnc); here we focus on **slot-family packaging** so estimators do not have to guess whether a 6.6 × 14 opening is a full-radius stadium slot, a square-end pocket, or a clearance oval drawn over an unstated pitch.
What slotted-hole DFM means for quoting
A **locating slot** names a width that the fastener or rail must follow, a length that is only travel or thermal clearance, and a position on a named datum. An **adjustment slot** usually makes the width the clearance dimension and the length the travel. Writing “slot for M6, position as needed” is not enough. Process pages for aluminum plate milling ([CNC 3-axis Al 6061 automation](https://3dwk.com/en/cnc-3axis/al-6061/automation.html), [CNC 5-axis Al 6061 automation](https://3dwk.com/en/cnc-5axis/al-6061/automation.html), [CNC 3-axis Al 6061](https://3dwk.com/en/cnc-3axis/al-6061.html)) assume the slot type is visible when lots mix dowel holes with adjustment slots on the same plate.
Do not bury “standard slots” inside a notes cloud. Put **SLOT A / B: 6.6 WIDE × 14 LONG, FULL END R 3.3, LONG AXIS // DATUM B, WIDTH LOCATES, LENGTH IS TRAVEL** 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), [flatness versus parallelism on CNC plates](https://3dwk.com/resources/flatness-vs-parallelism-callouts-cnc-plates).
Width, length, and end radius
A true stadium slot has end radii equal to half the width so a standard end mill can finish both ends. A boxed or square-end slot is a different feature: it needs a smaller cutter, a corner radius you actually name, or a later EDM step. If the CAD shows sharp ends but the note says “slot,” the shop has to guess. Keep slot width compatible with a realistic cutter; a 3 mm wide × 40 mm long slot in 8 mm plate is a thin, deflecting cut, not a free elongated hole.
Hole-to-edge rules still apply at both ends and along the flanks—see [minimum hole-to-edge distance](https://3dwk.com/resources/minimum-hole-to-edge-distance-dfm-cnc-plates). A slot that breaks a pocket wall or runs through a [counterbore land](https://3dwk.com/resources/counterbore-countersink-spotface-cnc-bolted-joints) should say so. Aluminum 6061 plate and billet $/kg planning bands sit in the common CNC aluminum range under **rates.v1.1** material tables; material cost is rarely the slot-family story—cutter choice, end-radius, and position scheme are.
Position, orientation, and mixed hole patterns
Name the long-axis direction from a datum, and say whether true position applies to the slot center, to the width mid-plane, or only to a companion [dowel pattern](https://3dwk.com/resources/dowel-pin-hole-location-dfm-cnc). A cover slot does not need the same scheme as a rail slot. [Position versus profile on CNC brackets](https://3dwk.com/resources/position-vs-profile-tolerances-cnc-brackets) belongs on the same sheet when a slot shares a pattern with tight holes.
Tolerance and inspection traps
Calling “slot for M6” with no width or end radius, mixing a stadium opening with a square-end pocket on the same note, or putting a tight true position on the travel axis, all force **needs_manual**. Default non-critical adjustment slots to a named width and a minimum length, and reserve tight position for the locating axis or for dowels. 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** plate with two labeled 6.6 × 14 full-radius slots versus a silent “M6 slots” outline on the same blank.
Example part walkthrough
**Example part:** Aluminum 6061-T6 plate ~100 × 60 × 8 mm, two slots 6.6 wide × 14 long with full end radius 3.3, long axis parallel to datum B, 12 mm minimum to the nearest edge, ISO 2768-m general, M6 adjustment travel only. With STEP + **SLOT A/B 6.6 × 14 FULL R3.3, WIDTH LOCATES, LENGTH IS TRAVEL, // B, MIN EDGE 12**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent “slots for M6, position as needed” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“standard slots”) versus a labeled width-length-end-radius pack and the clearer estimate path.
What widens bands fastest
Unlabeled mix of stadium and boxed ends, CAD sharp corners on a feature called a slot, missing width versus travel, and a slot that eats a dowel land or the plate edge. Quantity breaks help unit minutes but do not erase slot-family ambiguity—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [plate versus billet stock](https://3dwk.com/resources/plate-vs-billet-stock-cnc-aluminum).
What to do next
Mark each slot with a **width, length, end radius, orientation, and which axis locates**, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Packaging checklist: stadium versus boxed ends, edge distance, and any dowels that actually locate the plate. 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 slot-family questions rather than forcing a fake price.
Common questions
Is a slotted hole just an elongated clearance hole?
Only if you say which axis is clearance. Many drawings use a slot to locate in one direction and float in the other. If both axes are clearance, write that; if the width is a close guide, write the width and the position scheme.
Do the ends have to be full radius?
No, but full-radius ends are the default a mill can cut with a cutter equal to the slot width. Square or boxed ends need a named corner radius or a different process. Do not leave sharp CAD corners on a “slot” note.
Can I use slots instead of tight hole position?
Sometimes, for assembly adjustment. That does not replace a dowel or a tight pattern when the plate must repeat in a fixture. Name the locating features and keep the slots as travel.
How should I call out two slots that must stay parallel?
Give each slot a width, a length, and a long-axis direction from the same datum, and say whether parallelism between the mid-planes matters.