MSD spark plugs

[Car #4]

I got a set of these with a bunch of parts I got. Who made plugs for MSD? Also wondering what these might be for. They’re too short for any vehicle I own. Look more like lawn mower or chainsaw but why would MSD have plugs for that?

 

[Detective D]

Hard to say.
According to the internet, it is a 14mm thread with a .375" reach.
MSD lists off all of the classic manufacturers from the 60's and 70's.
I found an equivolent NGK with those specs, they do the same. According to the internet, it should fit anything from a poly motor from the early 60's to a 440.

LOL.

Who knew, you could swap a plug out of a 318 poly motor into a 425 Olds into a 383 Dodge into.....
It might be why they are sitting around. Someone may have ordered them and found out that, surprisingly, one size does not fit all and there they sat.

 

[Geoff 2]

I wouldn't use the MSD plug; it doesn't have a ribbed insulator.
The ribs extend the surface length from the terminal to the plug body. The increased length makes it harder for the spark to 'leak' away to ground.