KrakenPi CarBox — Fastener Schedule
Consolidated fastener list for the KrakenSDR + Raspberry Pi 5 car enclosure. Three printed parts: floor, frame, lid.
Related: carbox-enclosure-geometry-spec · krakensdr-pi5-reference-dimensions · krakenpi-carbox
Schedule — 36 fasteners + 8 washers
| # | Where | Qty | Screw | Engagement |
|---|---|---|---|---|
| 1 | KrakenSDR → floor | 8 | M3 × 16 button head | 10.8 mm into its tapped holes |
| 2 | Pi 5 case → floor | 4 | M2.5 × 8 pan head | 3.8 mm |
| 3 | Floor → frame | 12 | M3 × 8 button head | 6.8 mm into a 7 mm boss |
| 4 | Lid → frame | 6 | M3 × 12 button head | 10.6 mm into an 18 mm pilot |
| 5 | Car mount ears | 4 | M5 × to suit + 8 washers | through a 3 mm ear |
| 6 | Switch | 2 | Ø1.9 — usually ships with the switch | — |
Shopping list: 8× M3×16 · 6× M3×12 · 12× M3×8 · 4× M2.5×8 · 4× M5 + 8 washers
Why these choices
Button head, not socket cap. An M3 socket cap is 3.0 mm tall; the head recesses are 1.8 mm. Button head is 1.65 mm and sits flush. Every head was verified against its pocket. Only the lid screws stand 0.65 mm proud, which is cosmetic.
M3×16 for the Kraken, not 18. These replace the Kraken’s own M3×12 assembly screws. 16 gives 10.8 mm of engagement; 18 would want 12.8 mm and could bottom out in a hole tapped for 12.
M5 washers are not optional
The mount slots are stadium 5.5 × 12 mm through a 3 mm ear. An M5 head will pull straight through under load without a washer. Fender washers if available.
Don't over-torque the 18 self-tapping screws
The 12 joint + 6 lid screws thread into printed PC and pull against layer adhesion — 21 MPa versus 60 MPa in-plane. Snug, then stop.
No heat-set inserts
Every thread-forming screw goes directly into a Ø2.5 moulded pilot in the printed plastic. PILOT_D = 2.5 is the live value.
Not to be confused with 2din-enclosure-geometry-spec
The
carpi-2dinproject does use heat-set inserts (4× M2.5, 3.6 mm boss holes). This one does not. Easy conflation trap.
Possible upgrade: the lid gets opened repeatedly and self-tapped threads in plastic wear out after enough cycles. M3 heat-set inserts in the six lid posts would outlast that — but it needs PILOT_D changed from 2.5 to 4.0 and a frame reprint. Flag it only if the threads ever feel loose.
Hole, boss and counterbore reference
| Feature | Clearance | Head recess | Pilot |
|---|---|---|---|
| Kraken | Ø4.0 | Ø6.5 × 1.8, underside | — |
| Pi | Ø2.8 × 6.8 cross slot, ±2 mm both axes | Ø6.0 × 10.0 cross × 1.8 | — |
| Joint | Ø3.4 through floor | Ø6.5 × 1.8, from bottom | Ø2.5 × 7 deep |
| Lid | Ø3.4 through | Ø6.2 × 1.0, from top | Ø2.5 × 18 deep |
| Switch | Ø1.9 × 2 at 18 mm pitch | — | — |
| Ear slot | stadium 5.5 × 12 through 3 mm ear | — | — |
Printed bosses replace all standoff hardware:
| Boss | Spec |
|---|---|
| Kraken (8×) | Ø9.0, 4.0 mm lift |
| Pi 5 (4×) | Ø10.0, 3.0 mm lift |
| Joint (12×) | 10 × 8 × 7 mm block, Ø2.5 pilot 7 mm deep |
| Lid post (6×) | Ø8.5 × 44 mm, Ø2.5 pilot 18 mm deep |
Why the Kraken hole is Ø4.0, not Ø3.4
PC shrinks ~0.7%, which drags the 162.6 mm bolt pattern about 1.1 mm. The Kraken is aluminium and doesn’t shrink with it. ±0.5 mm of play absorbs the difference, and an M3 button head (Ø5.7) still bears fine. This is deliberate, not slop.
Provenance
Recorded 2026-08-26, in the session that finalised the three-part design. Two earlier lists exist and are superseded: an initial design proposal (said M2.5×10 and a Ø6.5 × 3 counterbore) and the v1 one-piece box (no joint screws at all).
Every number here is corroborated against the live constants in build_carbox_freecad.py. The list predates the FreeCAD port by ~3.5 h, but the port changed only geometry (BOX_W 145 → 186.5, CABLE_Y 131 → 168) — thicknesses, boss heights, counterbores, pilot depths and the 12-joint count are identical, so the schedule stays valid.
Master script: /Users/levander/Documents/sdr/KrakenPi_CarBox/build_carbox_freecad.py, mirrored to the CAD box as /exports/build_carbox_fc.py.
One open disagreement — lid screw length
The recorded spec is M3 × 12 (10.6 mm into an 18 mm pilot), which is what this note carries. A later derivation from the geometry suggested M3 × 16 (~14.6 mm engagement) as better for vibration in a car. M3×16 does fit the 18 mm pilot, so it’s a defensible change — but it is a proposed change, not the recorded spec. Decide before ordering.
Open items
- Resolve M3×12 vs M3×16 for the lid
- The rest of
projects/krakenpi-carbox/is stale — it documents an older revision (10× M3 joint, now 12; Ø3.4 Kraken holes, now Ø4.0;BOX_W145, now 186.5; 102 checks, now 125; 291.6 cm³, now 343.3; “Printed: ❌ not yet” when the frame printed 2026-08-27). Needs a documenter pass. - Test-fit the Kraken Ø4.0 and the Pi ±2 mm slot before committing to a frame reprint — no datasheet can confirm these