Measuring your frame for an A12

An A12 hub is held in the frame by bushings in the dropouts, and dropouts differ from frame to frame. From your values we select the bushings and spacers for each side — see The A12 system. For that we need the four values below, and a photo of each reading.

Before you start

Remove the rear wheel and have a digital caliper ready. Check whether your frame has a UDH: if it does, you can skip step 2. Not sure? See Does your frame have a UDH?

1. Brake side (left): dropout thickness
2. Drive side (right): dropout thickness. Not needed if your frame has a UDH.
3. Over Locknut Dimension (OLD): the spacing between the dropouts
4. Thread type and pitch of the thru-axle, for example M12 × 1.5

1. Brake side (left)

Measure the thickness of the left dropout at the point where the axle seats, as the red arrows show.

Measure at the axle seat

Do not measure the general plane of the dropout. We need the thickness at the exact point where the wheel axle seats against the frame.

Inside view

Outside view

2. Drive side (right)

Measure the right dropout the same way, at the axle seat, as the green arrows show. Skip this step if your frame has a UDH.

3. Over Locknut Dimension (OLD)

Measure the distance between the inner faces of the two dropouts, as the blue line shows: the space the hub fits into. On a thru-axle frame it is usually 142 mm or 148 mm, on a fat bike 177 mm or 197 mm.

4. Thread type and pitch

Check the thread of your original thru-axle. It is often marked on the axle, for example M12 × 1.5: 12 mm diameter, 1.5 mm pitch. If there is no marking, find the pitch with a thread gauge, or measure across 11 crests (10 pitches) with the caliper and divide by 10.

The pitch is the distance from one thread crest to the next, as the orange arrow shows.

5. Photos and sending

Take a sharp, close-up photo at each measurement point, with the reading on the caliper display visible: 4 photos on a standard frame, 3 on a UDH frame.

No.	Photo	What the photo shows
1	Brake side (left)	The caliper on the left dropout at the axle seat, reading visible.
2	Drive side (right)	The caliper on the right dropout at the axle seat, reading visible. Not needed on a UDH frame.
3	OLD	The caliper or a ruler between the two dropouts, reading visible.
4	Thread	The marking on the axle, or the gauge on the thread.
+	Drive-side dropout	Optional: only if you are not sure whether your frame has a UDH.

Send the values and the photos through the contact form, with the topic Converting an existing bike, and tell us whether your frame has a UDH. The photos can be attached to the message.

See also The check before a conversion.