Sorry if I seem a bit thick here.......I understand how a spark plug works but am mystified by "old" design thinking..........

Some older spark plugs (stripable type) feature 3 separate contact points for the central electrode...........

Others....(KLG for example) feature a pair of contacts..........

Modern plugs feature just one single contact..............

What was the theory/reasoning behind the design........?

They can't all spark at once. The spark comes from the closest / least fouled. Wasn't the idea that if one fouled or eroded, it would keep running ?

Did you see this older post of mine ? I have KLG KS5s and M80s with three, two or one side electrode...

http://pub37.bravenet.com/forum/static/show.php?usernum=3155626639&frmid=16&msgid=1302640&cmd=show

Missed that Rik ! Apols....must have been busy..........

I've found a couple of wartime-era NOS Champion L10 plugs still in the boxes.....the equivalent of the Lodge CN or C14 and the KLG F50...............

What's interesting about these plugs is that they have "WD" plus the arrow marked on the plug body........I've tested one in the W/NG and it performs perfectly........not bad for 70-odd years old........

Steve, can i see a picture of the box please? they are the same as used on an Austin Utility. any for sale?

I had a GSXR750 that you could get NGK spark plugs with two prongs.

Never really knew why two prongs.

It got stolen after only having it for six months, which was probably for the best.

email (option): sacombsashtrees@hotmail.com

None for sale Clive, but I'll do an image of the box...(in the workshop atm)...........

Maybe plug manufacturers by adding "prongs" were compensating for the unreliability of older fuels and/or components ? I don't know, but modern plugs today must have increased in specification and durability.............