# Machine Contact Medium

Adom **press-fit machine pin contact** (Medium) for the Adom modular electronics
system. A machine **contact** (`MC`) is a purely electrical receptacle pressed into a
plated through-hole on a molecule or scaffold. It accepts a machine **pin** (`MP`) tail, a
machine **needle**, or a bare wire, forming the solderless junction that carries power and
signals between molecules on the medium-class 2mm grid. This page carries the KiCad +
Fusion 360 `.lbr` library, STEP, and an interactive 3D view.

## What it is and where it goes

Medium machine contacts are the most common electrical interface on small and medium
molecules and on medium-class user scaffolds (which adapt the large base-scaffold grid down
to medium spacing). They carry power and signal between stacked boards. Unlike machine pins,
whose primary job is mechanical (the factory pincers grip them), a contact's function is
**purely electrical**. Medium contacts are pressed directly into the board, and also press
into the tops of medium machine pins so that pins, needles, and wires can be inserted into a
stacked assembly.

## Rating and wiring

| Property | Value |
|---|---|
| Current rating | ~6.4 A (80% derated) |
| Mating wire | 24 AWG solid core (precision-bent, enamel-coated) |
| Mates with | Medium machine pin tail (Ø0.51 mm), medium needle, or 24 AWG solid-core wire |
| Grid pitch | 2 mm within a row; separate rows at least 4 mm apart (pincer clearance) |

The rating is contact-limited (a medium machine pin can carry more, so the 6.4 A figure is
set by the contact) and is quoted at an **80% derating** for margin. The mating wire is
**solid core** (the enamel coating implies this, but it is called out explicitly).

## Mounting: press-fit into a plated through-hole

The contact presses into a **Ø0.78 mm plated through-hole** ringed by a **Ø1.30 mm** copper
annular pad. It is a solderless press-fit; solder-assist is available via the ring of 300um
jet-paste solder balls on the annular ring (Adom's
[solder-ball-layer standard](https://wiki.adom.inc/john/adom-solder-ball-layer-standard),
shown in the 3D view above, which also animates the press-fit insertion). The hole must be
plated and fabricated to the drill spec below.

## Dimensions

| Feature | Value | Source |
|---|---|---|
| PCB drill (plated, press-fit) | Ø0.78 mm | dims sheet + footprint |
| Annular ring (copper pad) | Ø1.30 mm | dims sheet + footprint |
| Accepts pin tail | Ø0.51 mm | medium pin tail (D5) |
| Head / flange OD | approx Ø1.4 mm | STEP / silkscreen |
| Overall body height | approx 1.7 mm | STEP |

> Press-fit hole sizes are still under validation (Caleb is testing). The Ø0.78 mm drill
> here matches the current dimensions sheet and the shipped footprint; confirm against the
> latest dims sheet before committing a fabrication.

## Files

- **Fusion 360 library:** `MachineContactMedium.lbr` (EAGLE/Fusion, round thru-hole pad + contact symbol)
- KiCad: `MachineContactMedium.kicad_sym`, `MachineContactMedium.kicad_mod`
- STEP: `MachineContactMedium.step`; web 3D: `MachineContactMedium.glb`
- Canonical adom-lbr JSON: `MachineContactMedium.adom-lbr.json`

## Provenance and related

- Original KiCad source: [`adom-inc/adom-kicad-library`](https://github.com/adom-inc/adom-kicad-library) (MachineContact + MachinePin).
- Dimensions: Adom "Machine Pin Dimensions" sheet. Usage and ratings: "White Paper: Molecule Design" (v1.0, September 2025).
- Mating pins: **[adom/machinepinmediumshort](https://wiki.adom.inc/adom/machinepinmediumshort)**, **[adom/machinepinmediumstandard](https://wiki.adom.inc/adom/machinepinmediumstandard)**.
- Larger sibling: **[adom/machinecontactlarge](https://wiki.adom.inc/adom/machinecontactlarge)**.