An apparatus for measuring strain in a polished rod of a beam pump unit includes a body having an upper wide section, a lower wide section, and a narrow section having a reduced width in comparison to each of the upper and lower wide sections. A bore is formed in the narrow section. The apparatus also includes at least two connectors configured to connect the body to the rod. The bore is positioned between the two connectors in a direction that is parallel to an axis of the rod. The apparatus further includes a strain gauge positioned in the bore, so as to measure strain in the rod between the two points of connection.