Champion Spark Plugs

[Curti]

These are the spark plugs used in 34-36 Auburn and Cord 810-812

[Dave Henderson]

Some H10 2 rib "coke bottle" plugs came with a screw-on top contact and others didn't.  I'm assuming the screw-on top TYPE was the earlier.  It also haS a less vivid coloring to the writing,  which was same coloration difference as the case for early/late Champion 3X plugs for the Model A Ford.  The plug on the left shows the top contact "nut" partially unscrewed. 
These are from a boxed set "Serviced by Nu-life Spark Plug Service of Pittsburg, guaranteed to render the same service as a new plug".  They apparently were carefully selected used plugs, cleaned up and re-blued.  To me they do look like NOS perfect.

[Curti]

Dave, all of the J6, J9 & H10 Champion two rib plugs that I have are screw on tops.  It is my understanding from a pretty reliable source that Champion converted from two rib to five rib in the 1947 - 1948 time frame.

[Dave Henderson]

Curt,  I have a 2 rib j8 that also has the screw-on top. 
I believe the '47-'48 time frame for the change to 5 ribs is good, maybe more so '48 than '47, or it could be that all versions weren't changed at the same time. 
Here's a question;  since the Champion 3X plugs that were original installations in Model A Fords had the knurling go all the way down, and the later "service Replacement" ones had knurling that stopped about 1 1/6" above the bottom, did all 2 rib H10's have knurling that didn't go all the way down or were there ones that did?  The center plug you picture almost looks like the knurling on it does go all the way down, but I may just be seeing rust pits.

[Curti]

Dave, the knurling stops at the bottom just like the other two.  My understanding is it took about two years for Champion to make the change over, it was a version at a time.