The fat ones are 19mm. If I had a marketing background, I'd say they were designed to warm up slower thus extending the warm up period mixture enhancement, and, at NO EXTRA CHARGE! In reality they were a mistake by the machinist reading the blueprint. They must be screwed in before the sheetmetal is installed. (But still NO EXTRA CHARGE!) Brad Mayeur
This was to be a reply the the CHT thread. Now I can't figure how to delete it.
Wiz at work!