Checkering files?

[Scota4570]

I like to checker the thumb piece on percussion hammers.  My old file is tired and to fine, ~36 LPI.   What is a good number of lines per inch to buy next time? 

[Metequa]

25 is coarse enough to give good purchase without becoming too tedious to apply.

[P.W.Berkuta]

Taylor did a post on a hammer that he checkered some time back - he did a bang-up job on it --- he is the guy you need on this .

[bobw]

The metal checkering files I have are 30, 40, 50.  I think there is also a 20 available on line. 30 is what I have used the most.

[Bob Roller]

Mine is a 20 LPI and it looks good and gives traction to a thumb which IMHO IS a safety feature.I have single pointed on a very few hammers and that is way too tedious and my eyes are like the rest of me,nearly 87.
Bob Roller

[Daryl]

I'm not sure, but I'd guess Taylor's is 24 to 30 LPI. Whatever it is, it's perfect. I think if too coarse, they look amateurish, as if done with a
3-corner file. They can bee quite fine and still work perfectly. It's to remove the smooth surface left by polishing & give some grip, not meant
 to cut your thumb.