How it connects
Straight push-in insertion. The bulb's two cylindrical contact pins slide into spring-tensioned internal metal contacts that hold the pins by friction and establish electrical contact.
Male and female halves
Female receptacle / lampholder with two pin entry sockets; mates with male bi-pin pins on a GU4 lamp cap.
Usually connects to
- GU4 bi-pin male lamp base
- MR11 halogen or LED bulb with GU4 base; MR8 halogen or LED bulb with GU4 base
Common sizes
- 4.0 mm center-to-center pin spacing (pitch); accepts pin diameters between 0.95 mm and 1.05 mm.
Where it is used
landscape lightinglow voltage track lightingrecessed accent lightingdisplay case lightingmarine and RV lighting
Variations
- Ceramic / porcelain round body lampholder
- Surface mount rectangular ceramic base
- Multi-pin universal sockets (compatible with G4 / GU4 / GZ4)
How to recognise it
Typically a heat-resistant ceramic disc or rectangular block featuring two small round or slotted pin holes spaced exactly 4 mm apart, often flanked by two brass rivet mounting eyelets and flying lead wires on the rear.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| G4 bi-pin lamp socket | Both share a 4.0 mm pin pitch, but standard G4 pins are thinner (0.65–0.75 mm diameter), whereas GU4 pins are thicker (0.95–1.05 mm diameter). GU4 pins will not fit into strict G4 sockets. |
| GU5.3 / MR16 socket | GU5.3 has a wider pin pitch of 5.33 mm and larger overall physical dimensions intended for MR16 lamps, whereas GU4 has a 4.0 mm pitch. |
| GU10 socket | GU10 uses a 10 mm spacing twist-and-lock base with wide peg ends for mains voltage, whereas GU4 is a straight push-fit miniature bi-pin typically used for low voltage (12V). |
Also called
GU4 socketGU4 lampholderMR11 bi-pin socketMR8 bi-pin socket
Good to know
Commonly found in 12V low-voltage luminaires using MR11 or MR8 reflector bulbs. In practice, many replacement sockets are universal ceramic holders with flexible internal spring contacts designed to accommodate G4, GU4, and GZ4 pins.
Related connections
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