Answer
The common difference of the sequence is

Explanation
The term "common difference" is telling us that our sequence is arithmetic. To find the common difference of an arithmetic sequence, we use the formula:

where
is the common difference
is the current term in the sequence
is the previous term in the sequence
In other words, the formula is telling us that to find the common difference, we subtract the previous term in the sequence form the current term in the sequence.
Let's find the difference for 1/6 , 1/3:
and




Let's make sure that the difference holds across the sequence by repeating the process for 1/3 , 1/2
and



And finally, for 1/2 , 2/3
and



We can conclude that the common difference of the sequence shown is
