What t f is a "stage 3 upgrade kit"?

[Jimmy Rocket]

Can any of you tech savvy captains explain what is meant by a "stage 3 kit"? And I suppose while you're at it info about "stage 2" and "stage 1" would be appreciated.

 

[dragline708]

deleted

 

[Jimmy Rocket]

Thank you all for the responses. And thanks Dragline for the explanation. Wiff the info is from ebay item #250046649669.

 

[ValknRocket]

They are referred to as Squawking Sparrows in my area.