Checkering?

[Samtech79]

Ok, help me wrap my head around this. Let's say 24 lines per inch; is it 24 lines per square inch or 24 lines per inch on one plain?
I ask because I assumed that it would be one one plain but when I went an measured the checkering on my rifle it is 12 lines per inch on one plain... And 12x12 on both plains that intersect at 90 degrees... So in a way, it's 24 lines per square inch.
The courses tools I can find at midway and brownells is 16 lines per inch.
Can someone who actually has the tools and experance chime in on this one please.
I'd like to add somemore to this rifle but don't want to waste my money on the wrong tools. If it really is per square inch 24, is a standard and I'm on the right track.

[G-forceJunkie]

Usually it is just how many lines in one plane. If there are intersecting planes, it would not matter. 20 and 30 lines per inch are common on metal, but too fine for wood. The 12 that your rifle exibits sounds about right for each plane.

[kcstott]

It's like threads per inch. 24 lines per inch would be .041" between two lines in the same plain. 12 LPI is very course. I don't see how you could have 12 line per inch unless it's impressed checkering. It is posible they were hand cut and hand spaced or machine cut.