GROHE Faucet Thread?

[Damon578]

I have a GROHE bathroom faucet that has seperate hot and cold twist nobs. The faucet has a single pipe that splits into two like an upsidedown T. Does anyone know what kind of thread comes on these?? I have tried 3/8 compression, I have tried 1/4NPT, it seems to fit better to the NPT however the thread is finer, so it still leaks!

 

[Plumber2000]

Should have been supplied with the flex tubes that make the connection between the faucet and the spout, use what was supplied.