John, The 18 MHz crystal is low profile but the 4 MHz crystal is not in the standard KPA100 kit. Yes, a low profile 4 MHz crystal should work OK in the KPA100, it is only used for the clock to the MCU. 73, Don W3FPR On 1/25/2014 3:50 PM, John Cooper wrote: > > Are both the 4mhz and 18mhz crystals low profile in kpa100? If not is low profile ok for 4mhz. > >