I saw that to, there are several flags.

 

Those blue welds resembles the sp515's that were defective. I always thought the weld process was damaging the porcelain of the sp515's . They were bad right out of the box . Ford never confessed what the problem was they just started issuing the sp546's that were beefed up .
I would not use a plug with those blue welds .

 

I saw that to, I opened all of them and one has the same design but no blue, weld.

Yes I am not going to use these.

So many flags on this one.

 

Wouldn't the welds be done prior to attaching the metal to the porcelain?

 

which one ?

 

Ebay.

 

can you post link to listing ?

 

I have no idea how plugs are assembled, we call it porcelain but its really ceramic . I don't know if its poured or what . The top is glazed fired . Is it poured into metal shell ,I doubt it . I would think the ceramic part is made separate then assembled to pieces if ceramic then welded . Ceramic glaze firing is done around 2200 degrees for a few hours , I doubt if the metal is subjected to that temperature. but the center electrode must be in the pour . I just assumed the metal was added in pieces and then welded

 

There simply are SOME things one shouldn't attempt to skimp on IMHO...I would never think of buying any sort of engine item on eBay...and suspect highly a lot of stuff on Amazon.

 

https://www.ebay.com/itm/8-Pc-Ford-M...-127632-2357-0