Some spark plugs come pre- gaped depending on the vehicle and type of spark plug. But even pre-gaped plugs should be checked with a feeler gauge to be sure it is correct
If the plugs you are using are not pre-gaped a feeler gauge must be utilized
in order to get an accurate gap reading. Your local auto parts store can help you with what the gap should be for your vehicle.
feeler gauge
0.03mm is the least count for feeler gauge
the clearance is measured at the top of the bearing with the help of a feeler gauge
The first generation of electronic ignition systems had a requirement to set the air gap between the reluctor and the pickup. It had to be set with a non ferrous metal gauge. That is why the brass blade in a feeler gauge set.
Adjusting the valves on a Caterpillar C 15 Engine is easy and does not take long at all. All you need is a wrench and a feeler gauge, You will then loosen up the bolt, place the feeler gauge in between the rocker arm and valve and then turn the wrench until the rocker arm touches the feeler gauge.
You just check the gap but usually they are good if new and for the right application. The gap is the air gap between electrode and ground strap. Just use a feeler gauge and they are typically anywhere from around .30-.65. To adjust, just bend electrode with a needle nose and recheck with feeler. There should only be a slight drag when pulled through not too tight. I have seen disc shaped feller guages about the size of a half dollar that go on a keychain. these you just turn until you hit the right number.
to measure spark plug gap
A .020" feeler gauge.
0,25 both regarding to the BOOK
A feeler gauge is actually a set of very fine strips of steel used to measure small gaps such as plug gap of an auto plug, or gaps in bearing surfaces.
.20 thousand on a feeler gauge
When was the last time you changed your spark plugs and wires? DO NOT USE A FEELER GAUGE ON THE PLUGS... THEY ARE PRESET AT THE FACTORY AND A FEELER GAUGE OR GAPPING TOOL WILL RUIN THE PLATINUM COATING.