A measuring device, but the Americans can get it by the kilo (5)
I believe the answer is:
meter
'a measuring device' is the definition.
(device for measuring something, eg a thermometer)
'the americans can get it by the kilo' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
The remaining letters 'mer' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'but' is the link.
Can you help me to learn more?
(Other definitions for meter that I've seen before include "Measuring device as for electricity consumption" , "Device for measuring and recording" , "Gauge" , "Device that measures, say, electricity usage" , "Apparatus for measuring" .)