The Canon EF-EOS M Adapter is the key to unlocking access to the vast array of Canon EF, EF-S, TS-E and MP-E lenses to the EOS M/EF-M compatible EOS cameras.
The Canon EF-EOS M Adapter mounts on an EF-M mount compatible camera (as a lens does) and allows a Canon EF, EF-S, TS-E or MP-E lens to be mounted on the other end. The Canon EF-EOS M Adapter is very solidly built, but it is a very simple device with no glass, one switch (the lens release) and electronics to allow the above-referenced lenses to fully-functionally perform on an EOS M camera body.
The adapter weighs 3.7 oz (105g) and measures 2.74 x 1.21” (69.5 x 30.7mm) without the additional .46" (12.9mm), 1.6 oz (45g) of the tripod adapter (included) attached.
The removable tripod adapter allows the camera balance to be shifted rearward when tripod-mounted (since the EOS M cameras weigh very little). Of course, the shift distance is not very big - and the size of the mount platform is quite small. A lens tripod ring is going to be a far better solution for tripod-mounting larger lenses - and no lens is too large for this adapter.