Was given a box of older parts. Among them was this chain. Is this inch pitch? There were no other drive train parts in the box so I can’t test it. And despite my age, inch pitch was no longer in use when I started ridding. Plates are stamped BD USA.

Skip tooth chain, similar one on ebay.
https://www.ebay.com/itm/38699244014...CABEgLfV_D_BwE

Yeah, inch-pitch. Looks low-miles, maybe even just shop-grime on a new chain? Some collector/restorer will probably pay decent money for it. Do you have a full bike's worth?
You can check for wear by measuring the full length, hanging from a nail at one end so gravity straightens it out. You don't need the length per se, but how far the last pin is past the nearest inch-mark. If all the pins fall exactly on inch-marks, then the chain is new or very low miles. A worn-out chain is something like 1/8" longer per foot, though you can still ride them like that.

For some reason that I don't understand, the cool trackies used to prefer block chain (ha ha the original block chain, before bitcoin!), and yours is not block chain. I see a couple block chains on ebay at the moment for $400 each! Personally I would rather have roller chain (like yours), and roller chain is the right stuff for any bike with inch pitch that's not a Match Sprint track bike. Prices not as crazy as for block chain.

Since I sold my '33 Excelsior, I have no bikes with inch pitch, so I'm not in the market. Check out The CABE, where there are more American heavyweight fans, though I'm sure we have a few here too.

I understand it was one of those folklore fads. Remember in the 1980s when we said a used steel frame was whipped (or whooped)? I'm sure we can think of all these fads that everyone understood. On example was the crank that was swaged to the spider.

Wide handlebars are best, no, narrow handlebars are best. Long cranks, no, short cranks. High pressure, no, low pressure.

so in inches, how low is a full bikes worth of chain? Counting links doesn’t seem like the way to go, given different link sizes

This is not exact but will get you in the ballpark:
Take the chainstay length of the frame and double it, example 17" x 2 is 34"
Take the teeth in the chainring and divide by two, example 26/2 = 13
Take the teeth in the rear sprocket and divide by two, example 10/2 = 5
Add those numbers, example 34 + 13 + 5 = 52". The real length will be slightly more than that. (The formula is exact when the F & R sprockets are the same size, which is almost never the case. Different sizes F&R requires a longer chain.)

https://www.ebay.com/itm/406121223549

Baldwin Duckworth branded inch pitch chain. They were sold with bikes new or in the cardboard box as aftermarket/repair parts. They're not especially rare or extremely valuable, but they do have some value if in good shape. The chain below sold for $90 in 2022. A two-tone Diamond chain in similar condition is more valuable and desirable for collectors of vintage American bikes. But the Baldwin Duckworth is still a good chain.

Thanks for the ID. Springfield, Mass apparently was home to basketball AND bicycle chains.