  Let $F_n$ be a free group of rank $n$, with free generating set $X$. A subset
$D$ of $F_n$ is a \emph{Distinct Difference Configuration} if the differences
$g^{-1}h$ are distinct, where $g$ and $h$ range over all (ordered) pairs of
distinct elements of $D$. The subset $D$ has diameter at most $d$ if these
differences all have length at most $d$. When $n$ is fixed and $d$ is large,
the paper shows that the largest distinct difference configuration in $F_n$ of
diameter at most $d$ has size approximately $(2n-1)^{d/3}$.
