Jet replacement

[thecanuck22]

I am needing to replace some of the jets in my hot tub. its really only the white part on the back, apparantly called the diffuser, that needs to be replaced on a few of them. The store is telling me that I have to replace the whole jet?!? cant you just purchase the white diffuser?
As well, how do you measure jets for replacement? How do I know if i have a 3" or a 3" 5/16......tape measure?
Thanks in advance.

 

[Melt In The Sun]

That's a good question...don't know the answer.