Please ensure you choose crystals that are the same range and frequency as those already fitted to your radio set - i.e. if you have a 27Mhz AM radio you must choose AQA crystals - the FM crystals wont work.
Please note - you CANNOT convert a 27Mhz to 40Mhz by fitting the "wrong" crystals - it just wont work. Equally you can't convert FM to AM by swapping crystals.
Futaba If you have a Futaba radio, Acoms crystals wont fit unless broken out of their holders - however, Tamiya crystals will fit.