Rear wheel spacers.

Hi
I dropped wheels out and took them to a bike shop to change the tyres to SM Distanzias.
The shop took the axles out with all the spacers that I had correctly put on (so I knew how to re-assemble).
There are 2 rear wheel spacers with dust caps, but of different sizes.

Does anyone know which side is which.

Thanks
Steve

Hi
I found the answer. Long one sprocket side.
Steve