my external flash is a Nikon SB600, the only diffuser i used on it was once at a sweet 16 and it was Shannon’s and it was something like this: http://www.bhphotovideo.com/c/product/749295-REG/Vello_VE_1001_Universal_Bounce_Diffuser.html

my studio strobes i diffuse with a soft box! 

:)