Harley Benton Parts String Action Gauge

Big downside: it's factory cut very bad, which means its edges are sharp. Especially with the fact that the rule is quite thin and made of steel, while your frets are usually alloy of softer metals. If you apply it to your frets, trying to check the level, for example - be prepared the frets will have scratches, and some of them may be quite deep (dents) the polishing won't help. Same stands for leveling the pickups - beware placing this ruler on top of your body finish, as it ends up with you having scratches there as well. So, while the idea of this ruler is great, the implementation and cheap "cutting" makes the deal not worth it.