TeX source:

\unitlength = 1mm \begin{fmffile}{simpletwo} \begin{fmfgraph}(60,45) \fmfleft{i1,i2} \fmfright{o1,o2} \fmf{fermion}{i1,v1,o1} \fmf{fermion}{i2,v2,o2} \fmf{photon}{v1,v2} \end{fmfgraph} \end{fmffile}