Slingerland Radio King tom or bass drum lugs - nickel

For sale are three Slingerland Radio King lugs in nickel finish.
I'd describe the condition as functional. These are not museum pieces. There's not much pitting on them, but the plating seems to be bubbling some. I've never seen this before and wonder if this was a manufacturing problem rather than a maintenance problem.
Then again, I'm not a Slingerland expert, so maybe you know better.
These look like Radio King center mount snare casings, except only one end has a swivel nut sticking out.
The hole spacing, center to center, is 2.25 inches.
Please feel free to ask questions!