Collection: Glass Fuses

Glass Fuse: The Pre-1980s Standard

Before the widespread adoption of the ATO blade fuse, cylindrical glass-bodied fuses equipped all automobiles and nearly all consumer electronics. They remain essential today for the maintenance and restoration of older vehicles (pre-1985 approximately), as well as for 12V/24V installations, RVs, boats, and certain industrial equipment.

A notable practical advantage: their transparent glass body allows for direct viewing of the filament — immediate visual diagnosis, without disassembly or a multimeter.

5×20 mm and 6×30 mm Formats: Do Not Confuse

Two formats coexist on older vehicles and equipment:

• 5×20 mm (5 mm diameter × 20 mm length) — the most common in Europe, on electronic installations and vintage European vehicles (Renault, Peugeot, Citroën, Simca…).
• 6×30 mm (6 mm × 30 mm) — common on American equipment and certain industrial machinery (generators, old machine tools).

The two are not interchangeable — always check the dimensions on the fuse holder before ordering. A simple ruler or caliper can be used to measure.

Fast (F) or Slow (T) Fuse: Which to Choose?

On glass fuses, two types of reaction coexist:

• Fast (marked "F" for Fast) — blows immediately at the nominal amperage. Suitable for sensitive electronic circuits (radio, ECU, sensors).
• Slow (marked "T" for Time-lag) — withstands a brief overload (1 to 3 seconds) before blowing. Suitable for motors and transformers that require a high starting current (windshield wipers, fans, electric pumps).

Always replace a fuse with the same type AND the same value — a fast fuse in place of a slow one will blow too often, while a slow fuse in place of a fast one will allow a dangerous surge for electronics.