I got a 60 degree fishtail gauge off EBay. It was made by Brown & Sharpe, Providence Rhode Island. Some questions on the markings:

1) There is no marking that denotes the angle, even though it is 60 degrees (I checked it against another gauge). There is a "650" at the point of the gauge, but I can't imagine what this means.

2) There is a set of markings "Double Depth of Amer Nat Thread". The number for 12 TPI is 0.108, whereas double depth of a 60 degree 12 TPI thread should be 0.144. Maybe someone can tell me what the different thread types are?

3) There are four scales on either side of the gauge - 14, 20 24, and 32. Each represents divisions of an inch - 14ths, 20ths, 24ths, and 32nds. What is this useful for?

1) There is no marking that denotes the angle, even though it is 60 degrees (I checked it against another gauge). There is a "650" at the point of the gauge, but I can't imagine what this means.

2) There is a set of markings "Double Depth of Amer Nat Thread". The number for 12 TPI is 0.108, whereas double depth of a 60 degree 12 TPI thread should be 0.144. Maybe someone can tell me what the different thread types are?

3) There are four scales on either side of the gauge - 14, 20 24, and 32. Each represents divisions of an inch - 14ths, 20ths, 24ths, and 32nds. What is this useful for?

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