Straight pins base guide

G4

Straight bi-pin

G4 is a tiny straight bi-pin base with 4 mm between pin centers. Many G4 fixtures are low-voltage and have very limited space.

Reviewed August 12, 2026

4 mm pin spacingNominal measurement · drawing not to scale

Connection: Straight pins
Electrical context: Usually low-voltage; confirm 12 V or 24 V
Also called: G4 bi-pin, 4 mm bi-pin, JC lamp base

How to identify G4

The two thin, straight pins are very close together.
Measure center to center, not outside edge to outside edge.
Read the old lamp for its voltage before buying an LED replacement.

Where it is commonly used

Puck lightsCabinet lightsLandscape lightsSmall desk lamps

Common use is a clue, not proof. The fixture label and model documentation take priority over a visual match.

Bulb shapes sold with this base

You may see these shapes with a G4 base. The base code does not guarantee the bulb width, length, beam angle, or clearance.

T3 capsuleJC capsule

Before you buy a replacement

G4 and G9 are not interchangeable.
Some LED replacements are too wide or long for the original cover.
Transformer compatibility can affect LED performance.

Not your base?See all base sizes →