When you see common sets of tools be it wrenches be it sockets be it whatnot, the metric sizes always include 10 to 19mm and the SAE sometimes stop at 3/4” which is the approximation of 19mm but more oft than not they run to 1”
So leads me to wonder what causes this and I came up with thoughts
maybe metric hardware uses smaller head to body ratio so a metric bolt with a 19mm head is about the same diameter bolt as a 1” sae head. I doubt this but it’s easy to confirm or dispute. I’d honestly assume the same head to body ratio.
could be sae is older cars primarily and older cars used bigger hardware with bigger bolts and cars got smaller over time and used smaller bolts so a newer car only uses up to 19mm heads on most things whereas older cars might run up to 1” heads for the same components. Of course on modern cars you got fastener bigger than 19 head but I mean like for the same component like engine bay mostly caps at 19mm heads
could be because metric don’t really use 20, or 22 or 23 as oft then to run 10 to 24 as your set introduces 3 wasted sizes whereas to run in 1/16 to 1” don’t waste since all sizes are used. And 25 is closest to 1” but that’s not used either
could be tools have gotten more expensive since the old days of sae so a 10 to 19 set today costs about the same adjusted for inflation as 3/8 to 1” back in the days so its like making the bag of potato chips smaller for the same price rather than raise the price. They made the tool set smaller and honestly people don’t miss it as much they can add in singles of 21 and 24 and be good.
So anyways I know that you can buy no skip sets from 10 to 24 but is most common to see sets like 3/8” to 1” and 10mm to 19mm and I’m wondering the reason.
So leads me to wonder what causes this and I came up with thoughts
maybe metric hardware uses smaller head to body ratio so a metric bolt with a 19mm head is about the same diameter bolt as a 1” sae head. I doubt this but it’s easy to confirm or dispute. I’d honestly assume the same head to body ratio.
could be sae is older cars primarily and older cars used bigger hardware with bigger bolts and cars got smaller over time and used smaller bolts so a newer car only uses up to 19mm heads on most things whereas older cars might run up to 1” heads for the same components. Of course on modern cars you got fastener bigger than 19 head but I mean like for the same component like engine bay mostly caps at 19mm heads
could be because metric don’t really use 20, or 22 or 23 as oft then to run 10 to 24 as your set introduces 3 wasted sizes whereas to run in 1/16 to 1” don’t waste since all sizes are used. And 25 is closest to 1” but that’s not used either
could be tools have gotten more expensive since the old days of sae so a 10 to 19 set today costs about the same adjusted for inflation as 3/8 to 1” back in the days so its like making the bag of potato chips smaller for the same price rather than raise the price. They made the tool set smaller and honestly people don’t miss it as much they can add in singles of 21 and 24 and be good.
So anyways I know that you can buy no skip sets from 10 to 24 but is most common to see sets like 3/8” to 1” and 10mm to 19mm and I’m wondering the reason.


