Here's the thing on tapping them on a hard surface... If you tap too hard, you ruin the electrode inside the shaft (which is the part that the plug wire attaches to) by either breaking it, or causing it to have a bad connection with the ground attachment when screwing it into your head.

Just be careful when you are or if you plan to tap it against something hard. The best tool to use to shrink the gapping of a spark plug is to use a newer-style gap-separator (which looks like a simple disc) and it should have a "gap shrinker" already attached to it.

Any questions, feel free to ask...you have an ASE-Certified tech right here if you need some simple advice...

 

Those disc style are new? they are older than me ... and I am older than you

 

^^^^ LOL!!!

 

Hey, yeah, there are two different styles from what I know of. I'm talking about the ones that look like ninja-stars...

 

Yep, I have one of those in my toolbox somewhere I think.. it is about 15 years old I think :D Not bashing you at all... just busting your b@!!s a bit they do work, but I typically have good enough luck using hand pressure as mentioned above.