I just started noticing these tooling marks recently when the light hit the kettle just right.
This kettle just happens to have a defect in the porcelain.
Seen this on several kettles too.
Here you can see them on both sides of the grate tab, sortof.
This is a kettle currently on the auction block but the lighting was perfect when they took the pics.
I believe in this generation the kettles were spun to form the semi-hemispherical part, then this section where the metal transitions from hemispherical into a cylinder of sorts for the top 2 inches or so, the tooling caused a bit of distortion, or maybe it happened when the man working the machine removed the kettle from the die. Frankly I dont know for sure but from my limited knowledge of metal forming that makes sense to me. I personally would be interested in seeing some pics or videos of what actually was done to make the MBH kettles & lids, at the Weber factory, but cant find anything from that era.
On the lid just above the rim you can see & feel the same type of tooling marks, distortion or whatever you wana call it. Unfortunately I dont have a good enough camera & lighting to take a pic of the lid so it can be seen. The spinning marks are visible to the eye but mostly un-photgraphable.
The tool marks are not on all MBH kettles but it makes me curious if there was a change in manufacturing process at some point and this was a side effect of that.
Im not implying the tool marks are good or bad, its just part of the manufacturing process with the technology they had in the day.
This is modern manufacturing process.
https://www.youtube.com/watch?v=d-hrjo-Qh5MThe spinning process for another kind of product.
https://www.youtube.com/watch?v=soCh9U2TU48