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Spark plug gap gauge


Well Known and Active Website User
VOC Member
After your reply I looked closer at the photo. Evidently Clark Feather wasn't the only manufacturer. Lisle, Snap-On, Mac, and Herbrand also made gap tools like that. They also appear to have given them the same model number of CF-71. Though there were some variations as some of the manufactures supplied them different ranges of thickness for the feeler wheel (I know what else to call it), but even then the model number was CF-71 and a letter or CF-70 and a letter. I might have to acquire one just for the novelty of it.

Mark Stephenson

Active Website User
VOC Member
I bought this gauge based on your location. A proper .18 gauge is not easy to find. I thought, how big a deal could it be as most gauges start at .20. I recently put some new NGK B7ES gapped with my old tool to .20 in my new to me 49 Series B. Not great on the starting, but flooding the engine probably did not help. Today, I replaced the plugs having gapped them to .18. Bike started first kick and it rode like a dream. I am dumbfounded by how big a difference .02 can really be. Its all a game of inches:)

peter holmes

Well Known and Active Website User
VOC Member
I very much doubt that the difference between 18 thou and 20 thou plug gap should make a discernible difference between starting and running, when running a Lucas KVF 50 mag I always erred towards 20 thou as that was the tolerance suggested by Paul Richardson's in his Bible, if the 2 thou additional gap is making a difference, to me it would suggest that something else is on the margins, but as you say, flooding and wet plugs never helps.

Pushrod Twin

Well Known and Active Website User
VOC Member
I use that style too, luckily. It skips .018", I use the .020, and I believe we struggle to feel the difference of .002" any way.
Yesterday I purchased a box of these Bosch 3 electrode types. They are a heat range or so hotter than the NGK BP6&7s I have been using in the hope that they will burn off at least some of the oil which sneaks downthe valve guides on my engine.
They are a curse to gap, that single wire tool is the best answer.


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Well Known and Active Website User
VOC Member
I have had this little baby since the late 1960's.
goes from 0.3mm to 1.1mm in 0.1 mm steps with thou also shown and includes gaping tool and aprobe to poke about inside the plug

Bosch part # EFKE5C



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