How do I identify what size of device I have when there is no longer a card in it?

Basically I am trying to figure out what size version of the device I have, a colleague of mine was in trouble with his phone so I gave him the card that was in the device.

Now I want the device back up and running but I am not sure what size card to get for it, hence the questions.

Any help on this will be greatly appreciated.

you can use the app to check the FW verison. See the FW post linked below

http://kb.sandisk.com/app/answers/detail/a_id/12713 

SanDisk Wireless Flash Drive 16GB/32GB
Firmware version is 3.4.1 (AO2S 1103) - Download firmware

SanDisk Wireless Flash Drive 64GB
Firmware version is 3.4.1 (AO2E 1103) - Download firmware