I bring loads of bits back, if they are not sharp I always put them in hand luggage rather than the case as I am in control of what happens to them. you will get pulled up by security in the airport in USA but if you explain what they are they are usually ok, trying to bring back 50 HPFP kits was hard to explain but I got chatting to one security guard about tuning his TFSi
If you put them in your case and wrap them up they will open it and open the package, chaeck what they are and probably do a swab on them, they may even remove them and leave a TSA card in the suitcase, unlikely but it does happen.