I have a grohe 3351 faucet. It has 3/8 solid chromed tube... what and where do I get fittings, flexible, for these. Do I crimp, compress or sweat these fittings

Hi Bob

You should just need to purchase a pair of 3/8" Female Compression Thread X 3/8" O.D. Male Compression Thread braided hoses (length as needed).

The male end with nut and ferrule goes on the chrome tube of the faucet and the 3/8" female end goes on the shutoff under the sink!

These are sold at all large home improvement stores that I know of... ;)

Mark