# 21 RW — Hypodermic needle gauge dimensions (OD, ID, wall thickness, dead volume)

For 21 RW, nominal o.d. (mm) is 0.81; nominal i.d. (mm) is 0.51; wall thickness (mm) is .152, verified against its source on 2026-08-27.

- **Gauge number:** 21 RW _(verified: appears in the quote below)_
- **Nominal O.D. (mm):** 0.81 _(verified: appears in the quote below)_
- **Nominal I.D. (mm):** 0.51 _(verified: appears in the quote below)_
- **Wall thickness (mm):** .152 _(verified: appears in the quote below)_

## What the source says

> 21     RW   0.81   0.81/0.83   .152   0.51   0.50/0.53

## Source

- https://nesmalltube.com/wp-content/uploads/2025/06/Metric_Chart_Web.pdf

Last verified: 2026-08-27. Review by: 2029-08-26.
Part of [Hypodermic needle gauge dimensions (OD, ID, wall thickness, dead volume)](https://referencesource.org/syringe-needle-gauge-dimensions/).