Fuel pressure question

[7duster4]

I have a rather stupid question. What exactly does a fuel pressure gauge do? I know obviously it reads the pressure for the fuel, but how do you know what a good psi is and if it's good or bad? My motor is a mildly built 318. I was thinking about ordering one from summit. I have heard they are nice to have. But what size fitting would I need for a 5/16 fuel hose? They seem to be all 3/8. Any info is appreciated, thanks.

 

[OHD]

To run the gauge into the car it will cost you about 300 bucks and the are not very accurate..

You can get a liquid filled small dial gauge and mount it on a regulator under the hood it you are worried about pressure.

The guages are 15-30 bucks.

I run one inside my little car and it is very rarely accurate and just fills up the hole.