What sometimes follows pieces of two-by-four? (5)
I believe the answer is:
eight
This clue is a double definition.
'what sometimes follows pieces of' is the first definition.
(as in 'pieces of eight')
'two-by-four?' is the second definition.
(eight is two x four)
(Other definitions for eight that I've seen before include "Carmina Burana composer" , "Hit, e.g. (anag.)" , "Where arrogance is needed" , "VIII" , "Number that figures in ice-skating?" .)