I don’t know , but I remember a story, probably apocryphal, from the ‘60s when Bill Keith was with Monroe, that Keith tried to play Earl’s banjo, but found the action too high to work for him.

1/8 inch is a good action at the 22nd fret.
The Masters of the 5String book lists Earl's 22nd fret action as 3/16,but lots players
play Scruggs style with 1/8 inch.

I think his action changed over the course of his career with different necks and heads on old -3. I heard that in the early calfskin-head days it was as high as 3/16" at the 12th, so like 1/4" at the 22nd. In the Master's book it's 3/16" at the 22nd, so like 5/32" at the 12th. In later days with the newest neck it was probably more like 1/8" at the 12th, so maybe 1/8"-5/32" at the 22nd.

One noteworthy thing is that many of the players in the Master's book (eg. JD Crowe, Allen Shelton, Buck Trent) had their action at 3/16" at the 12th fret. That's super uncommon these days.

Why guess? We have the answer, on page 39 of "Masters of the Five-String Banjo."

"3/16-inch over the last fret"

OK. That was as of the original publication in 1988. I can't say Earl's action never varied. But the table on pages 38-61 shows what the listed banjo players reported to Tony Trischka and Peter Wernick. Earl self-reported his preference for a somewhat high action. 

Note: While the column heading says "String height above 12th fret" I like how Earl ignored that and reported his action at the 22nd fret. I measure there as well, because that tells me with certainty the highest action anywhere on the neck. If you measure at the 12th fret, how much higher is your action at 17, 19 or 22? I'd say you don't know.

If the neck relief is different, the feeling of playability is going to be different even with the same string height measured at the same fret, whether 12th or 22nd.

The 12th fret provides an indication of the playability in the 5th-15 fret area.  22nd fret provides an indication of playability in the 17-22 fret area.

No reason why a player can't pay attention to more than one measurement, regardless of what metric is stated in the "Masters of the 5-String Banjo" book.  

quote:

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Originally posted by Phil - MO

1/8 inch is a good action at the 22nd fret.
The Masters of the 5String book lists Earl's 22nd fret action as 3/16,but lots players
play Scruggs style with 1/8 inch.

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Wow! That is really low. I set all my own banjos to 3/16 at the 12th. All banjos I repair and set up I do the same. I find any lower than 3/16 on my Gold Star, I get noticible string rattle on the mid to upper frets. I do tend to be a hard picker. I currently have it at slightly above 3/16 but I am going to adjust it down again.

I'm not sure if it Earls hand but in his original instruction book in the section on chimes it clearly shows his string height @12th fret.

I do remember Earl's action was high when I picked his banjo. It surprised  me. I never measured it or even asked. He played with such ease.