Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Drill (& gas orifice) sizes

Gordo Member Posts: 852
I was wondering how were the "number" (80-1) and "letter" (A-Z) drill sizes created or derived. None of my old mechanics books seem to have the answer. Thanks!
All Steamed Up, Inc.
"Reducing our country's energy consumption, one system at a time"
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Baltimore, MD (USA) and consulting anywhere.


  • Not sure but

    you might try asking the folks at Anderson Forrester who make the drills I am sure they have some history. Phone number 800-745-4466. I am going tocheck and see if they have a web site.
This discussion has been closed.