My thought is that they bought from more than one supplier and each supplier had their own set of molds. As long as the exterior looked the same, the mounting points lined up (so they were interchangeable), and as long as the lug was able to function without breaking, then Ludwig's primary concern would be the cost per unit. Over the years the trend has been towards thinner castings (less metal = less cost) but since Ludwig would have been ordering these by the thousands, and not discriminating between which ones they used any changeover from one style to another might take years before all of one type were used up. Just like the occasional outlier box of badges that falls outside the general track of serial numbers, there could be boxes of lugs on the bottom of a stack that didn't get opened for a year or two. During this time a drum could get a mix of different styles.

I toured the factory back in the 70's. I can assure you that no one was taking the time or trouble to discriminate between one lug over another. they were putting them together as fast as they could. I'd guess the thicker lugs were from earlier orders. Lugs got thinner because they found that they didn't need to be so thick to do the job which saved money, but they would still have to use up the supply of the older lugs and they didn't necessarily do so on a first-in first-out basis.

I actually think surface came up with the best scenario. I guess it seems to make the most sense.

While the random lug use seems most likely, it also seems that the possibility of them having been changed-out over the years is being ingnored. I received a Rogers kit earlier in the year where the ride and bass had the lugs changed-out and later lugs put on - heavy Dayton with felt to later Fullerton with lighter casting, thinner spring and no felt. Thus far I have 4 to go on the bottom of the bass to correct everything. I buy them when they are good and at the right price and set aside the Fullertons as I make progress. Hopefully I don't pass away before I finish and my wife sells them, someone gets them and starts interpretting why there are 4 Fullteron lugs on the bottom of the bass! In the meantime, if I sell them as is, I'll let you know about the deficiency just to avoid misinterpretation.

Yeah I'd agree that lugs swapped out over the years is the most likely scenario by a long shot. I wouldn't think you'd end up with more than a couple of styles on a single drum from the factory and even then it would only be at certain times when they were transitioning between lug styles and/or suppliers. I was just trying to explain one theory how the factory MIGHT end up putting two (or more) styles on a single drum.

there's undoubtably other ways it might have happened and the repurposed concert tom idea is certainly just as plausible ...but purposely using different thickness lugs for different parts of the drum defined by how much tension someone at the factory THINKS that part of the drum will be under has got to be the LEAST likely possibility.

I've taken many a Ludwig apart over the past 40 years and I've never noticed multiple style lugs on drums that I knew were totally factory original. And when I've needed to put lugs on a project shell I've never paid a bit of attention to the interior of the lugs when installing them. Whatever lugs I could source went on the drum. Figure a lot of people have done that over the past few decades.

The difference I've noticed is the length of the bolt shaft that goes through the shell. When they went to the thicker 6 ply shells they were longer. I found this out when I removed a lug on an 80's shell and tried to put it on a 3 ply shell. It stuck out on the inside of the shell.

As said above, most likely some lugs were switched out over time. Regarding concert toms... If I'm not mistaken, Ludwig used small classic lugs on all sizes of vistalite concert toms, large on 2 headed toms. You can always tell concert toms that have been fitted with bottom heads because the lugs are smaller.

Ya good point! With exception of floor toms. I've seen floor toms that were single head with large lugs. And bass drums as well.