Common Espresso machine port sizes (G vs M), tubes and fittings

Espresso machine have a wide range of sizes of pressure gauges, temp gauges, ports etc etc.

It can be a bit confusing.

They may connect to a boiler or the steam wand, or a pressure gauge.

There are a few fitting types to remember:

T & L

These are used to connect three or two tubes 

of the same size

Adapter or Nipple

This is an adapter.

These are used to connect two tubes (for example) of different sizes

This is a hexagonal nipple 

Straight 3/8 to 1/2 BSP.

It's nickel plated brass

Most espresso machines use BSP fittings and is sometimes called a pipe or G-type.

There are two versions: Parallel vs Tapered.

BSPP=Parallel / straight (this is the most common).

BSPT = Tapered.

These use imperial inches, not metric measurements.

The main difference between G and M threads is that G threads are a type of pipe thread, while M threads are a type of metric thread: 

G threads

Also known as British Standard Pipe Parallel (BSPP) threads, G threads are a type of pipe thread with a 55 degree angle and a constant diameter. They are cylindrical on the inside and outside, and are suitable for pressure-tight connections that are not sealed by the thread. G threads are commonly used in the water and gas pipe industries. 

M threads

Also known as ISO metric threads, M threads are specified in metric units (mm). The nominal size of an M thread is determined by the thread's major diameter and pitch.

The common sizes you will find in coffee machines are: G1/8", G1/4", G3/8", G1/2", M9, M12, M6, M10

Flair 58 - uses G1/8

Flair Pro2 - M9

E61 machines 

(like the Lelit v3, Rocket R58, La Marzocco GS3 and Profitec Pro series) - 

They use a M6 thread for the group head pressure/temp connector.

I use a BooKoo pressure sensor on my machine which uses a G1/8 thread. This makes it compatible with the Flair 58 or La Marzocco GS3.

The Bookoo came with an G1/8" to M6 adapter so it can work with my E61.

I've added a Pressure profiling Kit to my La Pavoni Europiccola.

This uses a G1/8 adapter

So the Bookoo pressure sensor fits onto it (without need for the G1/8 to M6 adapter).

Here are some other examples of adapters:

the M6 end is to the left. 

G1/8 on the right end

Pavoni Pressure Gauge Steel Nut M11

This adapter nut allows you to add a boiler pressure gauge.

The Pressure gauge has a 1/8" fitting.

1/8" = (8.6mm) Female

This stainless steel nut will convert La Pavoni models made after 1990.

Models made before 1990 will need a 1/8" to M12 (12mm) adapter.

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E61 Group Head Chrome Mushroom Cap

Slightly more coarse threads than the standard 3/8" British Standard Pipe thread. Chrome covered brass.

The most common thread size for a portafilter spout is 3/8 in BSP. The bottom of the portafilter body has 3/8" in female threads.

If you are pulling a shot and lack room for your glass between the drip tray and the bottom of the portafilter, just remove the spout.

The thread size for a 58mm portafilter handle is M10 or M12.

The thread is also 3/8" BSP

This is the steam valve on a Faema Faema from 1964. 

The thread size is 3/4" BSP

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Other thread formats:

NPT : National Pipe Thread 

National Pipe Thread (NPT) is a U.S. standard for tapered threads used to connect pipes and fittings. NPT threads are characterized by: 

Tapered: NPT threads have a tapered male and female thread. 

60° angle: NPT threads have a 60° thread angle. 

Flat crests and roots: NPT threads have flat crests and roots. 

Taper rate: The taper rate for NPT threads is 1⁄16 in (3⁄8 in per foot). 

Common sizes: Common NPT sizes include 1⁄8 in, 1⁄4 in, 3⁄8 in, 1⁄2 in, 3⁄4 in, 1 in, 1 1⁄4 in, 1 1⁄2 in, and 2 in.

NPT and BSP threads are not interchangeable because they have different thread forms, pitch, and flank angles. However, you can use an adapter to convert between the two