A plug that fits perfectly into a European socket won't necessarily fit — or fit safely — into a UK, North American, or Italian socket, even though all four regions use broadly similar-looking two-pin or three-pin designs. Plug and socket dimensional standards are genuinely regional, and a gauge built to one standard cannot verify compliance to another.
Why Regional Standards Diverge
Pin spacing, pin diameter, pin length, insertion force, and mechanical retention features (like the UK's requirement for a partially-insulated live and neutral pin) all differ by region — sometimes by fractions of a millimetre, which matters enormously for a go/no-go dimensional check. These differences exist for a mix of historical, safety, and regulatory reasons, and they aren't converging — a product sold into multiple regions needs separate compliance verification against each region's own standard.
The Major Regional Families
| Region/Standard | Plug type | Key distinguishing features |
|---|---|---|
| UK / Ireland (BS 1363) | Type G | Rectangular pins, fused plug, partially insulated live/neutral pins |
| Europe (CEE 7, VDE, EN 50075) | Type C/E/F | Round pins, varies by country (Schuko earthing clip, French earth pin) |
| North America (UL 498) | Type A/B | Flat parallel pins, polarised, grounding pin on Type B |
| Italy (CEI 23-50) | Type L | Round pins in-line rather than side-by-side |
Why a Gauge Has to Match the Exact Standard
A go/no-go gauge is machined to the exact dimensional tolerances published in its governing standard's own figures and clauses — for example, BS 1363-1's Figure 5, or UL 498's Figure 132.1. Using a gauge built to a different standard's tolerances, even one that looks similar, doesn't produce a valid compliance result — it's testing against the wrong reference dimensions entirely.
Practical Implication for Multi-Region Products
A manufacturer selling one plug design into multiple regions needs a separate compliant plug variant — and a separate gauge set — for each region, rather than assuming one plug design or one gauge covers multiple markets. This is standard practice, not a shortcut opportunity: regional electrical safety regulators generally require compliance evidence specific to their own published standard.