MTFCA Forum

What is the Autolite spark plug number for 1/2" thread base plugs? I have seen three numbers: F11 , #25 , and 3095.

O'Reiley auto parts under $5. Autolite 3095 I ran them for the last eight years. bobt

Sparkplugs.com

3095 $5.80

425x. $31.95

Thanks to both of you. I knew Champions had gone out of sight. I still have some NOS Champion A-25's. I wonder how they compare to Autolites?

Just one potential problem with Champion 25 is the electrode is just threaded into the ceramic and potted to the porcelain.

If you use more than finger tight on the thumb nut on the terminal, the potted electrode can be broken away inside and lead to hidden misfires.


Run the 25 in the Prus head and they work fine, normally gap at .025" as run on Ford magneto and good results.

Dan, Would there be a difference between Champion A-25's made at different decades? Is the electrode threaded on all of them? My box of NOS Champion A-25's were made in the 1950's or 60's, at the latest, and I never noticed the electrode issue. The have A-25, not just 25 on the porcelain and have more ribbing on the porcelain, If I remember correctly, but its been years since I looked at them.

My experience with the 25's was the same as Dan's. Mine were from the 90's.

Terry what color are the bases on your A-25? They are take apart right?
I have some I got in the 60’s that are cad plated. The 50’s ones I got are black or blued. Dan

Dan Hatch wrote: ↑

Wed Jan 28, 2026 12:54 pm

Terry what color are the bases on your A-25? They are take apart right?
I have some I got in the 60’s that are cad plated. The 50’s ones I got are black or blued. Dan

As best I remember, the bases were cadmium take a parts.

I've had a few of the terminals come loose from the insulator. I don't remember exactly what plugs they were. My car has "Silvery plated" Champion A 25 plugs in it. They have performed very well for over 15,000 miles.

Anyone had trouble with 3095 plugs leaking compression at the top metal crimp where it contacts the porcelain on the OD?

Are you sure it's a compression leak? Leaks at that point are unusual. Gray to black deposits are common on plug insulators, especially where rubber boots are used on the plug wires. It's caused by high voltage corona and will usually wipe off easily.