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God help me I'm back on @KatjaGrace's Women should be able to open things. A lady friend recently asked me for help with some bricolage/DIY; as a prelude to the work we needed to move a bunch of random assorted household stuff (furniture, technology, objets d'art, etc.) from one place to another, and we discovered that she struggled to lift almost any of it but somehow I (a fairly typical unspecial cis male) could lift all of it.
This made me think of the jam jar thing! It seems strange to me that almost-all jars and almost-all my friend's random possessions all fall into the gap between "typical female strength" and "typical male strength"? Back when the phenomenon seemed to be restricted to jars alone I figured perhaps one could write it off as "chauvinist jam-jar manufacturers tailor their lids for male strength"* - but it seems hard to argue for "chauvinist manufacturers of random household items tailor all the items' weights for male strength"!
(*Though I was unsatisfied with this explanation, even then, for other reasons)
So, what's going on? Could it just be that the gap between typical female strength and typical male strength is so huge that it's statistically probable for many ordinary things to fall between the two? I'm unsatisfied by this explanation A) because it doesn't really match my intuitive mental model of "typical male strength is probably around 1.25x typical female strength, not 3x it", and B) because I'm not an especially strong guy whereas my friend used to be a power-lifter when she was in university so I'd expect our gap to be smaller than the typical male-female gap.
So now I don't know what to think!
Your intuitive mental model of 1.25x is definitely underestimating the gap. It's much closer to 2x average for upper-body and grip strength (both are important for lifting), and can be more than 3x between specific people who are still well within 1 standard deviation of the means.
Your friend having been a power-lifter could help close the gap, but do note that women also lose muscle mass (and strength) quite a lot faster and more completely than men if they stop regular training. The main effect after some years would be due to general body type and keeping up habits of fitness, not any specific past activity.
I'm not into the weightlifting scene, but a first web search (take with a boulder of salt possibly too heavy to lift) yielded https://strengthlevel.com/strength-standards/male/kg showing average lift weights based on gender and either age or body weight. For example, male 30 year old beginner lifters' average bench press was shown as 49 kilograms while for female it was 19 kg, a ratio of 2.6x.
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