# Nut-trap gauge: M3 5.5 / 5.7 / 5.9 AF and M4 7.0 / 7.2 / 7.4 AF

> What nut-trap size does my 3D printer need for M3 and M4 nuts?

- Category: Stirling engines › Generators & instruments
- Kind: Hardware
- Basis: Hex traps stepped from the ISO 4032 across-flats (M3 5.5, M4 7.0) in 0.2 mm steps
- Page: https://xemstudio.com/objects/nut-trap-gauge/ · JSON: https://xemstudio.com/api/geometry?object=nut-trap-gauge · Plain text: https://xemstudio.com/objects/nut-trap-gauge/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- Every file on this site is drawn at exact size with no printing allowance; this gauge steps through sizes around the nominal so you can measure the allowance your process needs for one fit class, then apply it only to the features each object lists under Mating features.
- The gauge is an 80 × 24 × 5 mm plate with six hex traps on 13 mm pitch: M3 at 5.5, 5.7, 5.9 AF, 2.7 deep, and M4 at 7.0, 7.2, 7.4 AF, 3.5 deep.
- Press an M3 or M4 hex nut into each trap: the trap that holds it snug, minus 5.5 or 7.0, is your nut-trap allowance.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| gauge sizes | stepped around nominal | the true pin, nut, bearing or extrusion slot being tested | designed | all |

## Sizes

| trap | af_mm | depth_mm |
|---|---|---|
| M3 | 5.5 / 5.7 / 5.9 | 2.7 |
| M4 | 7.0 / 7.2 / 7.4 | 3.5 |

## Where the files are

- Wikipedia: [Engineering tolerance](https://en.wikipedia.org/wiki/Engineering_tolerance) — web — CC BY-SA 4.0 (text)
- Prusa: [Knowledge base: XY size compensation](https://help.prusa3d.com/article/xy-size-compensation_125045) — web — Prusa KB (verify at link)
- Long Earth Society: [Engine and rig builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/nut-trap-gauge/index.json

- nut-trap-gauge-m3-m4: [STEP](https://xemstudio.com/files/hardware/printer-calibration-coupons/nut-trap-gauge-m3-m4.step) · [STL](https://xemstudio.com/files/hardware/printer-calibration-coupons/nut-trap-gauge-m3-m4.stl) — nut-trap gauge: M3 at 5.5/5.7/5.9 AF, M4 at 7.0/7.2/7.4

## How it fits

### Connects to
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/): M3 (5.5 AF) and M4 (7.0 AF) nuts pressed into the traps

### Also needed
- [Hole gauges for Ø3, Ø5 and Ø8 (0.1 mm steps)](https://xemstudio.com/objects/hole-gauges/): the screw-hole allowance

## Questions

**What size nut trap for an M3 nut?**

The nut is 5.5 mm across flats; print this gauge and the trap that holds it snug, minus 5.5, is your allowance.

**How deep are the traps?**

2.7 mm for M3 and 3.5 mm for M4.

## Fits with

- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)
- [Hole gauges for Ø3, Ø5 and Ø8 (0.1 mm steps)](https://xemstudio.com/objects/hole-gauges/)
- [Nyloc lock nuts, M2.5–M8 (DIN 985)](https://xemstudio.com/objects/nyloc-nuts-metric/)