WB,
There are small size differances among the boxes for the various models. S&W made the boxes to fit each of them exactly and there were differances in frame size.
for instance, The 3 in Single action box was 7 3/4 x 3 1/8 x 1 1/4.
The 3" 32 Double Action box was 7 5/8 x 3 1/4 x 1 5/16.
The 3" Safety box was 7 3/4 x 3 1/2 x 1 3/8. For the 3.5 inch barrel length of each box in each model was increased by 3/8 of and inch. The 38 3.25 in barrel SA box was 8 3/4 x 3 3/8 x 1 1/2 (slightly shorter for the 3rd model 38 SA). The 3 1/4 inch Safety and DA boxes were exactly the sme size, 8 3/8 x 3 1/2 x 1 1/2 inches. For each inch increas in barrel length the box was increased in length by one inch.

I know that people will say that they stuck them in any box they had. And I think starting just before WWII that may have been true. But in the era that the old top breaks were made there was more attention to detail and fit and finish. Grips were fitted individually to each gun and boxes were made specifically for each model and barrel length, and were color coded for each model. I'm sure there were exceptions, but I believe they were few and far between. I've looked at literally hundreds and hundreds of Safety Hammerless boxes and have come to the conclusion that with the exception of the very first few years of manufacture up until the early 1890s S&W printed the caliber, model, and barrel length at the top of the operation instructions inside the top lid. I also believe that they started doing this with the 32 Safety Hammerless boxes a few years earlier than the 38 Safety boxes. I have found almost no 32 boxes without that info at the top of the inside of the lid. From what I can see, the 38 boxes started with the 3rd model or shortly thereafter. I have never found a 38 first model box with caliber and model name at the top of the instructions inside the lid. But there aren't very many 38 Safety first model boxes left to look at, so the evidence is inconclusive. I also have found it rare to find a Safety Hammerless box with out the end label. It is somewhat common to find the Single Action boxes and early DA boxes without the end label and my guess is that they improved the glue formula by the time they started making the Safety Hammerless guns. This is probably all more than you wanted to know. And it may be only the meanderings of an idle mind, but it came from a lot of observation, passion, and I hope logical thought process.
Mark

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Mark Connot