How do you know which preposition TO use in this and similar cases, is there any rule? As with prepositions in any language, experience is a teacher but you might find this webpage helpful! http://www.ego4u.com/en/cram-up/grammar/prepositions

Thomas, I know the usage from my experience. Let's look at "device for" and "device to" and study the context for each. Examples: I need a device to elevate the wire. I need a device for separating the seeds from the stalk. Let's find a device to separate the seeds from the stalk. Let's create a device for separating the seeds from the stalk. Where is that device for clearing the chamber and barrel? What is the device for clearing the chamber and barrel. What is the device for projecting visual images? If the device to project the visual images is broken, how can we continue our demonstration. (It all depends upon what you want to say my friend, and how you want to say it.

Hi, Tomas, In my opinion, 'device for' is a correct form. You can say, for instance, device for IPhone etc. I think in this case experience is more important than rules, as there are lots of exceptions to these rules. For me the most difficult thing in English is phrasal verbs. There are really lots of different combinations 'verb+particle' (e.g. carry on, carry out etc.), and sometimes only dictionary of phrasal verbs can help.