I have an MBA and am a CPA, CMA, and whatever...If I had it to do all over, I think I would have picked a trade and tried to really excel in it. I would love to have been a Norm Abram

. I am sick of staring at computer screens and am most happy working with my hands. That's how I have gotten into grill restorations.
Understood. I've watched Norm for years. He makes it look easy because he has the knowledge and skill to to do it right.
A guy like that is valuable. Unfortunately, in these days most people don't care about quality, only price. Fortunately, those that provide quality craftsmanship are in high demand and can name their price.
I restored a couple of old first generation Weber grills because they lasted 30 years without any real problems. They were expensive then, but they were made well.
I personally wouldn't have a new one if it was given to me. I'd sell it.
Oh, and getting back to your question.
I believe it's 1/4-20 as you found from the manual.
Cheers
Gerry