Hi Aharuray,

I don't know if I can help and you would be better off going to the RainBird website and emailing a request there. But I believe there is a tang (metal loop)that can be put in the up or down position. the down position gives you the variable circle. The tang hits bumpers of some kind either on the rotor bottom or in the rotor housing. These bumpers(usually metal also) can be adjusted by squeezing and rotating around the rotor stem to given the desired arc. If you go back where you purchased these heads, I am sure they would demonstrate how to adjust them. GL Aloha.

Bellow the nozzle area you will see two things that look like u shaped clamps with circles on each end and a u shaped with a square bottom object that moves between the two clamp like things (adjusters) by moving the u shaped clamps that is what adjusts the arc.

Here is a link that might be useful: do_it_your_self_site