- CHAMPION / http://www.championautoparts.com/
- BOSCH / https://www.boschautoparts.com/en/
- NGK / https://www.ngksparkplugs.com/
- Autolite / http://www.autolite.com/
- HARLEY DAVIDSON / http://www.harley-davidson.com/
- SPLIT FIRE / http://www.sf-j.co.jp/splitfire.html
- ACDelco / http://www.acdelco.com/
- DENSO / http://densoautoparts.com/
- The Green Spark Plug Co / http://www.gsparkplug.com/
- Changing Plugs / http://www.crosstownautocentre.com/
- Spark Plug Works / https://books.google.co.jp/books1946
- Crossreference / http://jp.sparkplug-crossreference.com/
- Spark Plug Colours / http://www.classic-car-magazine.co.uk/
- Spark Plugs History / http://au.bosch-automotive.com/
- History of the Spark Plug / http://www.spcoa.net/
- AC Plug Division / https://history.gmheritagecenter.com/
- BRITA HISTORY / http://www.brisk.biz/who-we-are/history
- First Spark Plugs / http://oldautonews.com/first-spark-plugs/
- NGK company History / https://www.ngk.com.au/ngk/history/
- Formula1 Dictionary / http://www.formula1-dictionary.net/
- NGK Technical Tips / http://www.cd-group.com/Components
- BG service / http://www.bgservice.com/54.html
- The Old Motor / http://theoldmotor.com/?p=135208