Anyone know what the difference is between the pfr6b & pfr6b-11??
Only because my local Halfords are doing the '-11 variety at half price....
Is it purely the gap size? I can't find anything on the web except that the '-011 has a 1.1mm gap??

You could get it from the horse's mouth: I've always had a quick & helpful response from NGK UK on this email address on the best plugs for my "classic" bike: technical@ngk.co.uk

rob the number 11 refers to the pre gap on the plug, i.e. 1.1mm

I had a query a few weeks back when I removed my plug with the letters PFR6G when I had the new PFR6B to replace them. Turns out the B is the newer plug.

see here for details

i bought the version 11's for my 93wrx ...it run like a bag of manure....having regapped them to ).7mm it runs fine..

yep, the 11 refers to gap size . 1.1mm

Sent e-mail to NGK.co.uk last night: Reply today (what great service!!):

The PFR6B and the PFR6B-11 are the same accept that the PFR6B-11 has a
wider gap (it is set to 1.1mm instead of the 'normal', narrower, 0.8mm).

To accomodate the wider gap, the side electrode is 'longer' so that even
though the gap is wider, the electrode is still at right angles to the
bottom of the plug.

Because the electrode is longer (and goes slightly further into the
combustion chamber) , it is not advisable to fit an extra wide gap type
plug in place of a traditional narrower gap type.

I hope the answer assists you.

Thank you for your enquiry.

Ron Merralls
Technical Services Assistant.

Unfortunately, they're not quite as helpful when you ask 'em for a set of Iridium plugs on long-term evaluation ;)

If you don't ask, you don't get, that's what my mum always told me :D