# Valve stem diameter (NA6)

Canonical URL: https://miatatorque.com/spec/valve-stem-diameter-na6/

Applicability: NA 1990–1993 (B6) — Other years inferred from 1990 factory evidence.

Confidence: fsm

Diameter
IN: 5.970–5.985 mm (0.2350–0.2356 in)
EX: 5.965–5.980 mm (0.2348–0.2354 in)

Always confirm against your factory manual. Match every restriction and follow all stages and procedure notes. Disputed claims must not be automatically resolved. The complete record below preserves every printed unit, source claim and procedure.

```json
{
  "id": "valve-stem-diameter-na6",
  "name": "Valve stem diameter (NA6)",
  "aliases": [],
  "applies_to": [
    {
      "gen": "NA",
      "years": [
        1990,
        1993
      ],
      "engines": [
        "B6"
      ],
      "note": "Other years inferred from 1990 factory evidence."
    }
  ],
  "kind": "non-torque",
  "value_text": "Diameter\nIN: 5.970–5.985 mm (0.2350–0.2356 in)\nEX: 5.965–5.980 mm (0.2348–0.2354 in)",
  "procedure": {
    "notes": "Measure the valve stems; intake and exhaust ranges differ."
  },
  "confidence": "fsm",
  "sources": [
    {
      "source": "fsm-1990",
      "page": "B–49 (PDF p. 76)",
      "as_printed": "Diameter\nIN: 5.970—5.985mm (0.2350—0.2356 in)\nEX: 5.965—5.980mm (0.2348—0.2354 in)",
      "verified_years": [
        1990,
        1990
      ],
      "document": {
        "id": "fsm-1990",
        "tier": 1,
        "title": "1990 Mazda MX-5 Miata Workshop Manual",
        "part_number": "1193-10-89C",
        "covers": [
          {
            "gen": "NA",
            "years": [
              1990,
              1990
            ],
            "engines": [
              "B6"
            ]
          }
        ],
        "url": "https://archive.org/details/1990-mazda-mx-5-miata-workshop-manual_202411"
      }
    }
  ],
  "jobs": [],
  "system": "engine",
  "component": "inventory-pass-2026-10",
  "componentName": "Service measurements and fasteners",
  "sequence_diagrams": [],
  "url": "https://miatatorque.com/spec/valve-stem-diameter-na6/"
}
```