Anyone know the difference between these Bosch spark plugs?

Try

The "+" at the end indicates the newer yttrium alloy electrodes, which I think will eventually supercede the versions without it.

The "L" instead of "D" seems to indicate a different protrusion length into the combustion chamber. I'm not sure what "D" means when it follows "L" though. An earlier catalog I've got suggests it might indicate two ground electrodes (180º apart) instead of one.

John

Yes, I've seen these in Halford's this morning.

According to one source, the D in FR 7L DC stands for length, (the F stands for diameter, the R stands for resistor, and the C stands for copper anode).

I agree about "F", "R", and "C". "7" is the heat rating, and the single letter immediately following it indicates "thread length and spark position". I take further letters to be qualifiers, and in this position "D" has the meaning of two ground electrodes.

On impulse, I've just googled for "FR7LDC" and "dual", and confirmed my suspicions.

John

Thanks.

I got through to someone at Bosch HQ in Denham (Bucks) who seemed to think the "L" stood for "semi surface" (or sub gap technology to enable plugs to fire when fouled).