The short answer
On housing and plate RFQs, **press-fit** (interference) and **slip-fit** (clearance) bores are not interchangeable hole notes. A press-fit bore is sized so a pin, bushing or bearing outer diameter stays put after assembly—hole size, roundness and finish all matter. A slip-fit bore is sized so a dowel or shaft assembles by hand or a light tap. Silence on **which fit family** and **which member is the controlled diameter** 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 aluminum housing RFQs where drawings say “press fit pins” next to “slip alignment” without labeling which bore is which. Illustrations use an **Example part** only—not a customer electronics enclosure. Related notes live in [press-fit pins and bushings in CNC housings](https://3dwk.com/resources/press-fit-pins-bushings-cnc-housings), [reaming vs boring for CNC hole size](https://3dwk.com/resources/reaming-vs-boring-cnc-hole-size), and [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands); here we focus on **press-fit vs slip-fit labeling** so estimators do not guess a drill/ream/hone sequence.
What each fit means for quoting
**Press-fit / interference** typically means the housing bore is slightly smaller than the pin or bushing OD, so assembly needs force or a temperature assist. Shops plan a reamed or bored finish, watch wall bulge around thin webs, and may ask whether the bore is the housing member or the pin member. **Slip-fit / clearance** means the pin should assemble without a press; the risk is slop and lost location, not crush. Process pages for electronics-thermal aluminum ([CNC 3-axis Al 6061 electronics-thermal](https://3dwk.com/en/cnc-3axis/al-6061/electronics-thermal.html), [CNC 5-axis Al 6061 electronics-thermal](https://3dwk.com/en/cnc-5axis/al-6061/electronics-thermal.html), [CNC 3-axis Al 6061](https://3dwk.com/en/cnc-3axis/al-6061.html)) assume clear bore-fit notes when lots mix open drilled holes with location-critical dowels.
Do not bury “press/slip as needed” inside a notes cloud. Put **Ø8 H7 PRESS BORE FOR BUSHING — HOUSING MEMBER** or **Ø6 SLIP DOWEL, CLEARANCE FIT TO PIN** 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).
Fit class, datum and which member
A fit class (ISO 286 style such as H7/p6, or an ANSI B4.1 equivalent) only helps when both members are named. Calling “H7” on a housing bore without saying whether the pin is p6, s6 or a purchased dowel leaves the interference unknown. Position of the bore pattern still needs a datum scheme—see [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts) and [position vs profile tolerances on CNC brackets](https://3dwk.com/resources/position-vs-profile-tolerances-cnc-brackets). Plate or billet stock can move residual stress after a dense press pattern; sibling context: [plate vs billet stock CNC aluminum](https://3dwk.com/resources/plate-vs-billet-stock-cnc-aluminum).
Aluminum 6061 bar/plate $/kg planning bands sit in the mid-commodity range under **rates.v1.1** material tables; material cost is rarely the fit story—ream vs bore, inspection gauges and thin-wall bulge notes are.
When a transition fit belongs
Use a transition fit when the assembly must locate tightly but still come apart for service, and you accept a mix of light press and light clearance across the tolerance stack. Say so explicitly (and name both members). For most housing buyers, splitting the pattern into **named press bores** for bushings and **named slip bores** for alignment dowels is clearer than one “close fit” note on every hole.
Tolerance and inspection traps
Calling “press fit Ø8” without max/min, mixing a press note on the housing with a press note on the mating pin (double interference), or asking for 100% air-gauge of every clearance hole without saying which bores are functional, all force **needs_manual**. Default non-critical holes to ISO 2768-m and put functional fit classes only on the press and slip families. Related: [CMM sampling plans for CNC lots](https://3dwk.com/resources/cmm-sampling-plans-for-cnc-lots), [surface roughness Ra callouts that raise quotes](https://3dwk.com/resources/surface-roughness-ra-callouts-that-raise-quotes). Bore finish (often a reamed Ra) belongs next to the fit class, not in a separate unmarked cloud.
Illustration 1 shows an **Example part** housing with labeled press bushing bores versus slip dowel bores on the same plate.
Example part walkthrough
**Example part:** Aluminum 6061-T6 housing ~80×50×18 mm, two Ø8 housing bores for press-in bushings, two Ø6 slip dowel holes, ISO 2768-m general. With STEP + **Ø8 H7 PRESS BORES (HOUSING MEMBER) FOR BUSHING; Ø6 SLIP DOWEL HOLES, CLEARANCE TO PIN; POSITION OF PATTERN TO DATUM A/B**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “all holes press or slip as needed” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“press/slip OK”) versus a labeled fit-class pack and the clearer estimate path.
What widens bands fastest
Unlabeled mix of press and slip on the same diameter callout, thin walls around a press bore with no bulge note, purchased-pin nominals that do not match the housing class, and 100% inspection of every open hole. Quantity breaks help unit minutes but do not erase fit-class 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 bore as **PRESS** or **SLIP**, name the fit class or max/min and which member is controlled, 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 fit-class questions rather than forcing a fake firm price.
Common questions
Is a press-fit bore always more expensive to quote than a slip-fit bore?
Often yes under **rates.v1.1** estimates, because ream/bore finishes and gauge checks take more planning than a drilled clearance hole. The bigger cost is silence—mixed notes without a class.
Can I write “H7 all around”?
Only if every hole truly shares that class and you name the mating member. Applying H7 to vent holes and press bores alike usually over-controls the part.
Do bushings and dowels follow the same habit?
Yes. Bushing OD-to-housing is one fit family; dowel-to-housing is another. See [press-fit pins and bushings in CNC housings](https://3dwk.com/resources/press-fit-pins-bushings-cnc-housings) for hardware selection—the bore label on the RFQ remains mandatory.
How should I call out bore finish?
Put Ra next to the fit class on press bores (reamed/bored lands). Leaving finish only in a general title block leaves the estimator guessing whether a drilled hole is acceptable.