Case size. The K4 is the same size as the KPA1500, which is slightly larger than the K3. So the SP4 height and depth match the K4, like the SP3 does the K3. 73, Lyle KK7P On 5/16/19 5:32 PM, Christopher Hoover wrote: > What's different between the SP3 and the SP4 besides the silkscreen ?