Spark Plug Gaping Tool

I saw this simple little spark plug gaping tool at my local big-box store the other day while I was browsing about.  It was inexpensive, less than $2.00 so I picked it up.  This gauge is two-sided, one being imperial graduations (thousands of an inch), the reverse metric.

The markings on the tool are difficult to read, so I highlighted them by coloring the graduations with a black magic marker.  I then wiped the ink off the surface using a shop rag and acetone, doing this twice to make sure the marks were well covered.  As long as you don’t get too aggressive with the surface wiping, this will leave ink in the recessed graduations and makes a big difference in terms of mark viability.

One other note, out of curiosity, I checked the accuracy of the gauge, using a good quality digital caliper.  I measured at the major graduation markings, i.e., .020, .030, .040, etc, all the way around.  Without exception, the tool measures between .004 and .005 too small, that is, .030 actually measured .026.  This was consistent all the way around the tool.

I suppose this is a clear example of you get what you pay for…