Q:

Subtle difference between ATtiny parts? 

I want to purchase 20 MHz ATtiny85 chips in SOIC-8 on a full reel from Mouser.  I found these two variants:

ATtiny85-20SUR
ATtiny85-20SHR

I have studied the specifications but cannot for the life of me find the difference between the two, and I don't want to order a full reel of the wrong part if there is any difference between them.  Does anyone know? 

A:

On page 13 of the datasheet, you can see the Order codes and what they mean. 

In this case, H and U mean the finish or plating on the pins. 

A:

From the datasheet, page 11:

Code indicators: H = NiPdAu lead finish, U/N = matte tin, R = tape & reel.