Available in 14, 16, 18, 20 and 22. Dents Per Inch.
Need a 7, 8, 9, 10 or 11 dent coil? Each of these can be used every-other-dent, so you can use the 20 DPI spring every other dent for 10 DPI.
How do you know what warp coil to use?
For Bead Weaving:
Place the beads you plan on weaving on a needle and measure an inch. Then, count how many beads are in that inch. The number of beads minus one is the warp coil that will be used. For example, if you are using Delicas you would find 19 11/0 Delicas are in one inch, so you would use the 18 dent coil. There is some leeway in this, and depending on the beads you are using, it might not work out perfectly (numerically), just close. Using a smaller (lower number) coil is better than using a larger (higher number) coil.
This is something you have to experiment with as a tapestry weaver. For finer weft, you will want to use a warp coil with more dents per inch. For thicker weft, you will want to use a warp coil with fewer dents per inch or even warp every other dent. (For example, an 18 dent warp coil every other dent is equal to a 9 dent warp coil.)