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you should find your gap size on the sticker under the hood and on the crossbar above the radiator, if you can still read it, or in your haynes manual. All you need are some feeler gauges and a pair of pliers to bend the tip. Most the time the gaps are already close enough not to worry about.
I figure anyone inclined to change their own plugs would also be incline to buy a service manual, but then again I see people trying to change out alternators, PS pumps, starters, AC compressors and change their oil and tranny fluid in the parking lot of AutoZone, asking questions every step of the way. I think some of these parts stores should just rent out garage space.
bigtig, to answer your question. the sparkplugs are gapped from where ever they come from, but while all the shipping and everything is happening, they get thrown around so much that the gaps closed up. that's why you always get sparkplugs that are too tightly gapped.
Bosch Plat +2's and 4's are gapped from the factory and dont require gapping. Personally for a Chevy, you should have bought the AC Delco Rapid Fire spark Plugs. ON the X though I use MOTOCRAFT Double platinums.
because the same size spark plug will fit more than one vehicle, I believe they "average" the gap of the vehicles, and that's how they're factory gapped. That's why most need to be gapped before actually installed.
When I put Bosch +2's in, I didn't bother with the gap like I had when I did the generic champions a while back. If you look at the electrodes on each one, you'll notice that the Bosch has a very different looking platinum electrode. It's almost like a white cone with a piece of platinum inside, rather than just a short, little cylinder of platinum on others. I figued not to mess with it because their engineers probably know something I don't.