Abstract: Screen deck assembly 10 has a locking system for retaining a plurality of modular screen panels 20 in such a manner that they can be individually replaced, if desired. The system includes sets of abutting retainer bars 18 which each have half of a generally cylindrical opening 28 which is adapted to receive generally cylindrical sleeve members 30. The sleeve members extend through the retainer bars and also through openings 14 in underlying support frame members 12. Locking pins 32 inserted into the sleeve members expand the lower portions of the sleeve members to lock the retainer bars relative to the support members. Sideways separation of the abutting retainer bars is prevented by downwardly extending continuous annular ring portions 72 on the sleeve members which are seated in complementary semi-circular grooves 61 formed in each of the abutting retainer bars.