Motorcycle mirror threads: M8, M10, right-hand and left-hand

Handlebar mirrors almost always screw onto an M8 or M10 thread (1.25 pitch, or 1.5 as on many BMWs), either standard or left-hand. To find out which one your bike has, unscrew the original mirror and measure the stem: 8 mm is M8, 10 mm is M10, and if you turned it clockwise to unscrew it, the thread is left-hand.

Motorcycle mirror threads

The thread code tells you two things. The number after the M (metric) is the stem diameter in millimetres: M8 means 8 mm, M10 means 10 mm. The second number, when there is one, is the pitch: the distance in millimetres from one thread to the next. M10x1.25 and M10x1.5 have the same diameter but a different pitch, so they do not screw into each other.

Then there is the direction. A standard (right-hand) thread screws in clockwise; a left-hand thread (marked SX or LH) works the other way round, screwing in anticlockwise. On FAR product pages you will find it under the thread specification.

How to measure the thread in 2 steps

1. Unscrew the original mirror and measure the stem with a caliper: 8 mm = M8, 10 mm = M10. If there is a lock nut at the base, loosen it first.
2. Check the direction: did you turn it clockwise to unscrew it? It is a left-hand thread. Anticlockwise? It is a right-hand thread.

Check both mirrors: on some bikes the two sides do not have the same thread. If the mirror does not move in the direction you expect, do not force it: try the other way.

And the pitch: 1.25 or 1.5?

On motorcycles the most common pitch for M10 is 1.25; 1.5 is typical of BMW. If in doubt, compare the stem with a thread gauge or with a screw whose pitch you already know. A wrong pitch shows straight away: the screw jams after one or two turns. Stop and do not tighten.

Left-hand thread: which side?

There is no single rule. Each manufacturer decides which side gets the left-hand thread, and sometimes changes it from one series of the same bike to the next. Some examples from FAR product pages:

• Piaggio Liberty and Vespa LX: the left mirror has an M8 left-hand mount (FAR 8225). On the Liberty 150 MOC 2V 2009-2013 Piaggio fitted both left-hand and standard thread mirrors (FAR 6027): check yours before ordering.
• Honda X-ADV: up to 2020, with the original Honda adapter, the thread is M10x1.25 left-hand; the FAR 7058 and 7059 replacements (standard M10x1.25) screw onto the handlebar support once the adapter is removed. From 2021 the FAR 8215 and 8216 replacements have an M10x1.25 left-hand thread.

That is why FAR product pages always show the thread and the mounting side, as seen by the rider sitting on the bike.

Adapters: when you need them

If the mirror you like does not have the same thread as your bike, first check what is in the box: many FAR universal handlebar mirrors already include mounts for several threads. The Gravity, for example, comes with a screw kit for M8, M8 left-hand, M10x1.25 and M10x1.25 left-hand. If that is not enough, there are adapters:

An adapter lengthens the mount: the mirror sits a few centimetres higher. On some Honda models the original mirrors are fitted with specific adapters; in that case the M10 diameter alone is not enough, and the upper thread and the usable length of the stem also matter. All adapters are in the Adapters and Spare Parts collection.

How to see it on the FAR website

• Search by Motorcycle, at the top of every page: choose make, model and year and see only the products verified for your bike.
• “Before you buy” box on the product page: with your bike selected it says “Screws onto your mount” or warns you about a different thread; without a bike you get the “Measure it in 2 steps” link.
• Technical specifications: the thread and its direction, and the mounting side.

If your bike is not listed, see Can’t find your bike?. To find out whether a mirror is road-approved, read the guide to approved mirrors.

See handlebar mirrorsSee adapters and spare parts

Frequently asked questions

How can I tell whether my mirror thread is M8 or M10?

Unscrew the original mirror and measure the stem diameter with a caliper: 8 mm is M8, 10 mm is M10. Then check the direction: if you turned it clockwise to unscrew it, the thread is left-hand.

What does a left-hand (LH) thread mean?

It is a thread that screws in anticlockwise and unscrews clockwise, the opposite of a standard one. On FAR product pages it is marked as left-hand or LH.

Does the right mirror always have a left-hand thread?

No. It depends on the bike and sometimes on the series: on the Piaggio Liberty, for example, the left-hand thread is on the left mirror. Always check your original mirror and the product page.

Can I fit an M8 mirror on an M10 mount?

Only with the right adapter. Many FAR universal mirrors already include mounts for M8 and M10 in the box: you will find it in the thread specification on the product page. Never force a screw into a different thread.

What is the difference between M10x1.25 and M10x1.5?

The diameter is the same, 10 mm, but the pitch is different: 1.25 mm versus 1.5 mm. The two threads are not compatible. M10x1.25 is the most common on motorcycles, M10x1.5 is typical of BMW.