A sprinkler and side-loading nozzle insert assembly includes, in a preferred arrangement, a sprinkler body provided with a flow passage along a sprinkler body axis and a nozzle insert spring-loaded received in a complementary recess formed in the sprinkler body. The nozzle insert has an axis of rotation transverse to the sprinkler body axis and is rotatable from an insertion position to plural operating positions. The nozzle insert is provided with an elongated, substantially cylindrical insert body including a nozzle bore extending through the insert body on an axis transverse to the axis of rotation and alignable with the flow passage in at least two of the plural operating positions. Plural index tabs extend radially from the insert body at circumferentially-spaced locations, and are adapted to engage respective plural index notches in the sprinkler body as the insert body is rotated to the plural operating positions.