diff --git a/spoolman/prometheus/metrics.py b/spoolman/prometheus/metrics.py
index 3995ff6..3963c57 100644
--- a/spoolman/prometheus/metrics.py
+++ b/spoolman/prometheus/metrics.py
@@ -91,5 +91,6 @@ async def filament_metrics(db: AsyncSession) -> None:
             row.color_hex,
         ).set(1)
         FILAMENT_DENSITY.labels(str(row.id)).set(row.density)
+        FILAMENT_DIAMETER.labels(str(row.id)).set(row.diameter)
         if row.weight is not None:
             FILAMENT_WEIGHT.labels(str(row.id)).set(row.weight)