[TheForge] 2 tapping questions, oops 3

[Barking Crow]

I was doing some tapping yesterday and came across a reference to sharpening
the tap.  Anyone know how to sharpen a tap?

2.  In my collection of taps from E-bay there is one 11/16 x 11 N S.  Now I
know National Coarse, NC, and National Fine, NF, and National Pipe Thread,
NPT, and Metric, but not NS.  What does the N S stand for?

3.  One of the taps has no flutes or spaces in the cutting teeth, but the
cutters are continuous 360 degrees.  What is it?  I have some retreading
taps and they don't look like that.

Thanks for any help.

I was surprised and pleased how well some old taps from the junkyard worked
after I got the rust off.

Jeff Valentine