Went to France last year, made it to London with half a trad rack in my carry-on.  They made me check the baggage because of a suspicious looking nut tool.  They didn't make me pay for the extra checked baggage on that flight.     
  
On the way home I carried a set of nuts and cams and put the offending nut tool in my checked baggage.  They didn't like the looks of my #11 nut and made me check the bag.  That cost me $100 extra.   
  
To avoid future hassles and $ I will always check metal climbing gear on international flights.