The short answer
On a CNC RFQ, **blind** and **through** holes are not the same quote package. Through holes usually mean chip exit, tool break-through risk, and possible backside burr notes. Blind holes mean depth-to-diameter, chip packing, bottom style (flat vs drill point), and often a different tap or ream plan. Silence on hole type is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the hole diameter itself.
This guide is for buyers packaging prismatic and turned RFQs. Illustrations use an **Example part** only—not a customer fixture. Related hole sizing lives in [reaming vs boring for CNC hole size](https://3dwk.com/resources/reaming-vs-boring-cnc-hole-size) and [deep-hole / gun-drilling CNC](https://3dwk.com/resources/deep-hole-drilling-gun-drilling-cnc); here we focus on **how to label blind vs through** so estimators do not guess.
What “blind” and “through” mean for quoting
A through hole exits the opposite face (or into a cavity that fully clears the tool). A blind hole stops at a controlled depth. For quoting, also say whether the exit face is a free exterior, a sealed pocket floor, or a mating boss that cannot show break-out marks. Process pages for aluminum robotics and automation parts ([CNC 3-axis Al 6061 robotics](https://3dwk.com/en/cnc-3axis/al-6061/robotics.html), [CNC turning Al 6061 robotics](https://3dwk.com/en/cnc-turning/al-6061/robotics.html), [CNC 5-axis Al 6061 robotics](https://3dwk.com/en/cnc-5axis/al-6061/robotics.html)) assume clear hole-type notes when lots mix fasteners and fluid passages.
Do not bury “Ø6 × 12 deep somehow” inside a GD&T paragraph. Put **BLIND** or **THRU** next to each critical hole 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).
Depth, L/D and chip exit
Blind holes with high length-to-diameter ratios raise pecking, chip evacuation, and tool-breakage risk. Soft stock (PA66 time coeff ×0.8 under **rates.v1.1** estimates) still packs chips in deep blinds. Harder alloys (17-4PH ×1.4, IN718/IN625 ×2.5, CoCr ×2.2) amplify heat and peck time; deep blinds on hot alloys frequently auto-route toward **needs_manual**, especially when the line mid exceeds configured planning bands (e.g. above ~$2000 for hot alloys/CoCr).
Through holes help chip exit but create break-out and backside burr notes—especially on thin walls or near cosmetic faces. Say whether a slight break-through witness is allowed.
Bar $/kg planning bands (estimates only): PA66 ~5, 17-4PH ~9, IN718 ~55, IN625 ~60. Material cost is rarely the hole-type story—depth control and secondary ops are.
Threads, inserts and finish sequence
Blind tapped holes need usable full-thread depth plus unused runout or tip clearance. Through tapped holes need exit-face protection if anodize or plating follows. If you want cut taps versus wire inserts, name the family—see [Helicoil vs tapped holes for CNC aluminum](https://3dwk.com/resources/helicoil-vs-tapped-holes-cnc-aluminum) and [designing threads and tapped holes](https://3dwk.com/resources/designing-threads-and-tapped-holes). Type II anodize after threading needs sequence notes; leaving critical bores as-machined until after anodize is a separate finish decision.
Tolerance and bottom-style traps
Tight true position on deep blinds forces probing strategies. Flat-bottom blinds are not free—they often need an end-mill finish pass after a drill. Default non-critical hole sizes to ISO 2768-m and put functional tolerances only on locating or sealing holes. Related: [surface roughness Ra for machined parts](https://3dwk.com/resources/surface-roughness-ra-for-machined-parts), [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts).
Illustration 1 shows an **Example part** with a labeled through fastener stack versus a blind tapped boss with depth and bottom callouts.
Example part walkthrough
**Example part:** 6061-T6 plate ~100×60×18 mm with six M4 through clearance holes (THRU, free exit, light deburr OK) plus two M5×0.8 blind tapped bosses, usable thread 8 mm, drill depth 12 mm, flat bottom preferred, ISO 2768-m general, boss true position 0.1 to Datum A. With STEP + clear BLIND/THRU labels, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “tap all holes somehow” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“holes as needed”) versus a labeled blind/through block and the clearer estimate path.
What widens bands fastest
Unlabeled mix of blinds and throughs, “deep as possible” blinds without L/D limits, conflicting cosmetic no-break-out notes on thin exits, and 100% CMM of every hole wall. Quantity breaks help unit cost but do not erase depth risk—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 every fastener and fluid hole **BLIND** or **THRU**, state depth / usable thread / bottom style, 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 hole-depth questions rather than forcing a fake firm price.
Common questions
Can I mark every hole “through” to simplify quoting?
No. Mislabeling blinds as through creates wrong tool plans and often scrap or **needs_manual** clarification. Label what the CAD actually requires.
Do blind holes always cost more than through holes?
Not always—shallow blinds can be cheaper than thin-wall throughs with cosmetic exit rules. Depth, L/D, thread type, and finish sequence drive the **rates.v1.1** band more than the word “blind.”
How do hot alloys change deep blind quotes?
Pecking and heat in IN718/IN625/CoCr raise machine-time under **rates.v1.1** coeffs (×2.5 / ×2.2 estimates). Expect wider bands or manual review when L/D is aggressive.
Should weep / vent holes follow the same rules?
Yes for labeling. Function notes (vent vs drain vs fastener) still help—see [vent, drain and weep holes on CNC housings](https://3dwk.com/resources/vent-drain-weep-holes-cnc-housings)—but BLIND vs THRU remains mandatory.