The Dillon 1050 Shell Plate #2 is used to load .38 Spl ammo, and similar calibres, on the Dillon Super 1050 (and older RL 1050) progressive reloading machine. When the shell plate is indexed it moves each case progressively from station to station to complete the loading process.
Consult the reloading machine's manual for the appropriate shell plate for your calibre.