Water supply line size 3/8 inch or 1/2 inch?
If you are using a kitchen style faucet it is a flow restricted type and will not need piping larger than the 3/8" tubing normally recommended for this application.Smaller sinks like kitchen sinks, toilets, and bathroom hand washing sinks work okay with the supply lines being 3/8" OD, (1/4" ID nominal size). Consequently, this size pipe (tubing) is the standard in the industry today, since all of these devices use some type of flow restrictors mandated by government regulations (big brother). Laundry tubs however are exempt from these regulations today, and can be piped with standard 1/2" copper pipe (tubing) or what ever size you choose to use and reduced or increased at the faucet. Fitting size at the faucet is dictated by the manufacturer. Most single supply home piping is 1/2" copper at the wall penetration, or this new and better (cheaper) supply tubing. My laundry tub faucets are piped with 1/2" copper which allows the sinks to be filled quickly. If the faucets you are using are new look at the instructions supplied with the faucets for their recommendations for connection size and type.