Targus ExpressCard ACP60US User Manual page 6

Targus ExpressCard Notebook Docking Station with Digital Video and Audio
Using the Spacer Connector
A spacer is supplied to ensure the proper fitting of the 34mm
ExpressCard into a 54mm slot. This spacer has no functionality
other than to prevent any movement of the card once it is inserted
into the 54mm slot. The spacer is not needed if you have a 34mm
slot on your notebook (see the diagram below as to the two different
slots that are currently shipping in today's notebooks).
The spacer simply snaps on to the existing ExpressCard and is
inserted with the card connector into a 54mm ExpressCard slot.
Carefully align the spacer with the ExpressCard and join the two
pieces together by locking the clip in place.
Please make sure that the clip is firmly secured and that there is
no gap between the two components as shown in the diagrams
above.