String highth at the nut,

[banjo1]

My mando has small fret wire.I do not know that highth of the fret and want to lower the action to a level somewhere below the stratosphere.
How tall is the fret wire(flat fingerboard)above the fingerboard?

How much clearence do I need to be safe?

How much above the 1st fret highth do I file the stringnut groves?

[sunburst]

Fret wire is available in different heights, and it usually gets some filed off after installation, so I don't know how tall your frets are.
But that's OK, because it doesn't matter. The nut height needs to be set to the height of the fret, no matter how tall it is.

Here's an easy way to measure:
Press a string down at the 3rd fret. When you do that, the string goes in a straight line from the nut slot to the 2nd fret. While holding the string down against the 2nd and 3rd fret, check how far it is from the 1st fret. There should be just a little bit of clearance. You can barely see it, so I press down on the string over the 1st fret and see if it moves before hitting the fret. It should just move, and shouldn't be touching the fret already. You can also listen as you tap the string down against the 1st fret. If it is moving, you can hear a little ping as the string hits the fret.
If the string is higher than that, file the nut slot 'til it's right, and then you have 7 to go.

Note that new strings will be higher for a little while, 'til they finish bending over the edge of the nut, so if I am setting up an instrument with new strings, I do two things;
1. press down firmly on the string right where it leaves the nut. That bends it a little bit and gets it closer to where it's going to end up.
2. set the height a little higher than I would if the strings were not new.

[Martin Jonas]

Frank Ford has an excellent page on precisely that question at frets.com. Much the same as John has said, but it helps a lot to have Frank's photos to go with it.

Martin

[banjo1]

Thanks guys.
You all are a lot of help.