Guide to Light Fittings, Caps and Bases

What Are the Different Types of Light Bulb Fittings, Caps and Bases?

Quando si sostituisce una lampadina, choosing the correct light bulb fitting, cap, O base is just as important as selecting the right brightness or colour temperature.

IL cap (also called the base) is the part of the bulb that connects to the light fitting. It provides the electrical connection while securely holding the bulb in place. Since different fixtures are designed for specific bulb types, manufacturers have developed a wide variety of light bulb bases to ensure only compatible lamps can be installed safely.

Whether you’re replacing a household bulb, a spotlight, or an LED tube, this guide explains the most common light bulb fittings, caps, e basi to help you find the right replacement.

Tappo a baionetta

Bayonet caps are easy to recognize thanks to their push-and-twist locking mechanism. They remain popular in the UK, Australia, New Zealand, and several other countries because they are secure, affidabile, and simple to install.

BC B22 (Tappo a baionetta)

Diametro: 22mm

Pin-to-Pin Diameter: 27mm

Height: 26mm

IL BC B22, also known simply as B22, is the standard bayonet cap used in many household light fixtures. It features two locating pins that lock into the socket with a short twist.

Le applicazioni comuni includono:

• Plafoniere
• Lampade da tavolo
• Lampade da terra
• Lampade da parete
• Decorative fixtures

Because of its durability and ease of installation, B22 remains one of the most widely used light bulb fittings.

SBC B15 (Tappo a baionetta piccolo)

Diametro: 15mm

Pin-to-Pin Diameter: 17mm

Height: 26mm

Allo stesso modo, IL SBC B15 (Tappo a baionetta piccolo) works in the same way as a B22 but is smaller in diameter.

It is commonly found in:

• Illuminazione decorativa
• Applique da parete
• Illuminazione degli elettrodomestici
• Small table lamps

Although most B15 bulbs operate on mains voltage, some specialist versions are designed for low-voltage applications.

Other Bayonet Variants

In addition to B22 and B15, several specialist bayonet fittings are available, compreso:

• B22d-3 – Often used in Fireglow and industrial mercury lamps
• BY22d – Commonly used for low-pressure sodium (SOX) illuminazione

Edison Screw Cap

Unlike bayonet fittings, Vite di Edison (ES) caps screw directly into the socket. Named after Thomas Edison, they are now the most widely used light bulb bases worldwide.

ES E27

Diametro: 27mm

Height: 26mm

IL E27 Edison Screw is the standard screw fitting throughout Europe, Asia, Australia, and many other regions.

Tuttavia, it is often confused with E26. Although the difference is only 1mm, the two bases are designed for different electrical systems.

• E27: 220–240 V
• E26: 110–120 V (America del Nord)

Always check both the fitting size and operating voltage before purchasing a replacement bulb.

SES E14 (Piccola vite Edison)

Diametro: 14mm

Height: 26mm

For smaller fixtures, IL E14 Small Edison Screw is the preferred choice.

You’ll typically find E14 bulbs in:

• Lampadari
• Lampade da parete
• Decorative pendant lights
• Illuminazione degli elettrodomestici
• Illuminazione d'accento

Grazie alle sue dimensioni compatte, E14 is especially popular for decorative LED filament bulbs.

Common Edison Screw Sizes

Capsule Lamps

Compared with standard bulbs, capsule lamps are much smaller and use two metal pins instead of a screw or bayonet fitting.

The model number simply refers to the distance between the two pins, making it easy to identify the correct bulb.

This design also prevents bulbs with different voltages from being installed in the wrong fixture.

G9 Base

Spaziatura dei perni: 9mm

IL G9 fitting is designed specifically for 220–240V mains voltage.

You’ll commonly see G9 bulbs used in:

• Lampade da parete
• Decorative pendant lights
• Lampadari
• Illuminazione sottopensile

Oggi, LED G9 bulbs are widely available and provide an energy-efficient replacement for traditional halogen capsules.

G4 Base

Spaziatura dei perni: 4mm

Per confronto, IL G4 fitting operates on 12V and requires a compatible transformer or LED driver.

G4 bulbs are frequently used in:

• Cabinet lighting
• Display lighting
• Illuminazione del paesaggio
• RV and marine lighting

GY6.35 Base

Spaziatura dei perni: 6.35mm

IL GY6.35 capsule is another low-voltage fitting designed for 12V or 24V sistemi.

It is commonly installed in:

• Illuminazione del compito
• Lampade da scrivania
• Display cabinets
• Illuminazione d'accento

Fortunatamente, LED versions are available for all these capsule bases, making upgrades simple while significantly reducing energy consumption.

Linear Halogen

R7s Fitting

Cap Diameter: 7mm

Bulb Length: 78mm or 117mm

Unlike capsule lamps, R7s linear bulbs have contacts at both ends.

They are widely used in:

• Floodlights
• Security lights
• Work lights
• Uplighters

When replacing an R7s bulb, always match:

• Lunghezza
• Potenza
• Voltaggio

This ensures proper performance and safe operation.

Halogen and LED Spotlights

Spotlight bulbs are identified by the distance between their pins and the locking mechanism. Di conseguenza, different spotlight bases are not interchangeable.

GU10

Tipo: Intrecciare & Lock

Spaziatura dei perni: 10mm

Operating directly from 220–240V mains power, IL GU10 is the most common spotlight fitting used in residential and commercial lighting.

Nowadays, LED GU10 bulbs are available in various:

• Wattages
• Beam angles
• Colour temperatures
• Brightness levels

making them ideal replacements for halogen spotlights.

GU5.3 / MR16

Tipo: Push Fit

Spaziatura dei perni: 5.3mm

Unlike GU10 bulbs, MR16 (GU5.3) spotlights require 12V power supplied by a transformer or LED driver.

They are commonly installed in:

• Kitchen lighting
• Display lighting
• Retail lighting
• Illuminazione d'accento

GZ10

A prima vista, IL GZ10 looks almost identical to a GU10.

Tuttavia, there is one important difference.

The GZ10 uses a dichroic reflector, which directs heat backwards rather than forwards. Di conseguenza, the base has a square profile that prevents it from being installed in fixtures not designed to handle the additional heat.

Compatibilità

• ✅ GU10 → fits GU10 and many GZ10 fittings
• ❌ GZ10 → should not be installed in GU10-only fixtures

Fluorescent Tubes and LED Tubes

Both fluorescent and LED tubes use two-pin caps at each end. Tuttavia, different tube diameters require different base types.

G13 / Q8

Tube Diameter: 25mm

Spaziatura dei perni: 13mm

IL G13 fitting is the industry standard for T8 LED E tubi fluorescenti.

After inserting the tube, simply rotate it to lock it into place.

The same fitting is also used on:

• T10 tubes
• T12 tubes

G5 / T5

Tube Diameter: 16mm

Spaziatura dei perni: 5mm

Nel frattempo, G5 fittings are designed for slimmer T5 tubes.

These compact tubes are widely used in:

• Uffici
• Espositori per la vendita al dettaglio
• Illuminazione sottopensile
• Illuminazione commerciale

The same cap is also found on some T4 fluorescent tubes.

Considerazioni finali

Insomma, identifying the correct light bulb fitting, cap, O base is essential before purchasing a replacement bulb.

Whether your fixture uses a B22 bayonet, E27 Edison Screw, E14, G9, GU10, MR16, R7s, O G13 fitting, selecting the correct base ensures a safe installation and optimal performance.

Finalmente, if you’re replacing an older incandescent, alogeno, or fluorescent lamp, consider upgrading to an LED equivalent with the same fitting. Not only will you enjoy lower energy consumption, but you’ll also benefit from a longer lifespan, reduced maintenance, and improved lighting efficiency.