While the Bosch plugs come pre-gapped, it is a good idea to check the gap before installing the plugs. You never know, could be the box had been dropped, and it just happened to land on the electrode end, now it is now longer gapped to spec compliments on gravity and inertia. You can pick up a gapping tool for a song, throw it in your toolbox and use it for ever.
There are a number of style from the simple siding ramp gapper, to the fixed loop type. All you need to do it determine what gap you want, then place the proper sized loop between the electrode and center post, if gapped correctly you should feel just the slightest resistance as both points make contact with the gapping tool. If no resistance is felt, gently close the gap, if you cannot get the proper size loop in the gap, gently open it up. Some tools have a "H" shaped prong for opening the gap when necessary.
It is more difficult to explain how to, that it is to do. You will learn the proper "feel" shortly, that only experience can provide.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.