I think they are better described as "insulators". i did find out what the small piece is (I think) I read this at fixit dot com: Note that there is a rubber guard on the edge of the logic board where the Digitizer and LCD ribbon cables bend over the logic board. Make certain it is there...

I hope this is in the correct forum... I'm very familiar with the disassembly of the iPhone - that is not the problem. What happened was - two small black items fell out during my last assembly - don't know where they go. Here is a pic of them:

Old guy here. EE degree, retired. Quite familiar with Electronics. Retired from Motorola. Hoping I can help someone folks here - and also will need some help on my iPhone 4... :-)