I see that the knurling itself must have been a different knurling attachment on the lathe. It looks like the fine knurling knob is chromed while the other bits are nickel. The coarse knob is nickel plated, with other nickel plated parts attached. I'd like to agree that it is simply replaced, but that's a weird part to lose. Maybe it was a school drum. Our school's drums were subject to all kinds of jerry-rigging to cover for lost parts.

I should have stated that those pictures are not of a drum that I own. Just examples from ebay and reverb.

It would have been a different knurling tool for sure.  Slingerland seems to have mixed and matched chrome and nickle parts in areas that people weren't likely to notice. I have seen lots of auction examples of the tension adjustment plates where the knob was clearly chrome and the plate was nickel.  The knob is pressed onto the shaft so it would probably be pretty hard to remove it or have it just fall off. It also seems that they improved the quality of their chrome plating at some point in the late 50s. Some of their earlier chrome plated parts were not nearly as smooth and shiny as later parts were.

To me, the coarser knurling seems like an improvement, but they went back to finer knurling in the 60s. It could also be that they used both at the same time off and on. That same basic knob was also used for their mufflers, for years, It just had a threaded through hole machined in it. They also used it on the Epic pedal for spring tension. 

To complicate things even more, all of these drums are over 70 years old so a lot could have happened to them over that time. It is clear in some auctions that the strainer is not original to the drum for various reasons so that makes pinning down these details difficult.

Is there a "quote" feature?  Responding to thin shell's first post:  Thin shell, I agree in principle with your research.  I have found the same thing:  50's 3-point snare drums with the fine knurled adjustment knob.  My question also is what year this changed to the coarse knurling.  How did you arrive at '57?  '57 drums can be quite tricky to distinguish from '55/'56 or '58/'59 drums.         

I have looked at so many different auctions that it's hard to say exactly, but I have seen several SlingerLeedy Reliance and Utility snares, which came with the Slingerland 3 point strainer, that are date stamped with a '57 date and that appear to be drums that haven't been tampered with, all seem to have the coarse knurling.  55 is the last year for the dogtag brass badge on the Slingerlands, and most of the student radio kings, and non "Super" Krupa snares with that badge, seem to have the fine knurling. Again, it's not exact because parts could have been swapped over their life, but the dogtag badged drums that appear to be all original all seem to have fine knurling. So really I should say '56 or  '57 is my best guess on when the coarse knurling first came out.

I've never seen a '57 date stamp on a Slingerland drum.  I haven't thought to look at the Leedy line in those years.  By chance do you have a link to a '57 Leedy with date stamp?  The "dog tag" badge actually carries over into '56 (per Dr. CJW and Brooks Tegler).  I don't have anywhere near enough data but what I am seeing is in line with your findings.

I went back and looked at some of my notes. I have a Leedy Reliance that a friend found with a pile of MIJ drums set out for the trash in the mid 80s. At that time I didn't know anything about Leedy, but it did have a date stamp in it and as memory serves it was either '57 or '58. It was a real mess, having been covered with naughyde and had extra holes where a Ludwig P85 had probably replaced the original three point strainer. Unfortunately in my ignorance at the time, I sanded, stained and Polyurethaned the interior so my date stamp is long gone. I have sought pictures of identical drums over the years and any pictures I have with a date stamp seem to be '58 or later. So it is my observation that '58 might have been the first year they started date stamping their shells. If that's the case, then the absence of a date stamp, and the presence of a straight arm on the strainer, dates the drum as most likely a '57. 

There is a Leedy Reliance that is on Reverb being sold by Donn Bennett. He lists it as a '57, but he says the date stamp is too smudged to read. It has a picture of the stamp through the hazy snare head, and I have adjusted it and cant really make it out but it looks more like an 8 than a 7 at the end of the stam.  It does however, have a three point with coarse knurling and a screw on, twisted snare arm on it.  According to Dr CJW, '58 was when they started using the twisted snare arm, so if that is accurate, that drum is actually a '58.

I have come across one period picture that I am pretty sure is a knob with coarse knurling. It is a picture of Gene Krupa, taken on March 25, 1957. While the picture is not 100% clear, it does look like coarse knurling and it has the then new, black and brass badge so this drum is probably a '56 or an early '57 drum. I had to search the Page code for the site where this is posted to get the high res photos to get this crop from it. 

That's what I have at the moment. 

thin shell, you probably remember this Gene Krupa set that sold at auction a while back.  It included a "dog tag" badge snare with sound king lugs ('55-'56).  In the video at 55:30 is a real good look at the throw off with coarse knurled knob.  More data points are needed but somewhere in the '55-'57 timeframe seems likely.

https://www.youtube.com/watch?v=CitMN_Dbbwo

Sorry, can't seem to attach an active link to the post.  User error or site issue?

That is a good point. I went back and rewatched that video, and it is definitely a coarse knurling knob. As was pointed out, that entire drum set was from August of '54 because he took it to Australia the same month. The problem I have, is that the picture was taken last year, and the history of that set is murky, so we don't know if it is original to the drum or it Gene swapped it out at some point, or if it was swapped out later after he owned it. We don't even know how long Gene kept it after he stopped using it in public.  So it is a data point, but most of the drums of similar vintage seem to have the fine knurling, or has obviously had the strainer replaced at some point, so you can't really say for sure if the details are correct.