Abstract: A screen printing apparatus includes a plurality of novel printing mechanisms, one each at the outer end of a radially disposed support arm having a first, elbow joint and attached at the inner end of the arm to a vertically disposed, rotatable hub. Each printing mechanism includes a screen frame clamp pivotably mounted at a second, vertically pivotable wrist joint to a base section, allowing pivotability of a screen held in the clamp. The base section has attached at an outer end thereof an alignment bar having a plurality of upwardly protruding registration pins. A transparent calibration plate has holes therethrough adapted to insertably receive the registration pins, in an overlying relationship to an object to be printed on a platen beneath the calibration plate.