\nThe following is by my understanding.<\/p>\n
\nI recall buying a socket one time to remove the anode of a hot water heater. It was, I think, one-and-one-sixteenth. I bought it from a discount bin, and it came on a straight bar. I was in a hurry, so didn’t think much of it.<\/p>\n
\nLater, I had to buy a 15\/16″ socket to undo an oil filter casing. The clerk asked me what drive I was using. I didn’t know. The socket was 1\/2″ drive. He assumed, correctly, that I would need an adapter from 3\/8″ drive to 1\/2″.<\/p>\n
\nBack then, I just had a standard socket set from Mastercraft. It had both 1\/4″ and 3\/8″ drives, and its largest socket was 3\/4″. It hadn’t occurred to me that bigger drives – for instance, 1\/2″, were called for sometimes. However, when I got home from buying the 15\/16″ socket, I inspected the one-and-one-sixteenth socket, on its bar, that I’d bought years ago to remove the water heater anode. Indeed, that socket, too, was 1\/2″ drive.<\/p>\n
\nWhen I thought about it, the reasoning was obvious why 1\/2″ drive might be called for: a bigger fastener might well mean it’s under more strain, so needs to be tighter. In turn, a larger-diameter drive would be stronger, so less likely to break when removing such a fastener.<\/p>\n
\nIt turns out that, for 3\/8″ drive, the torque range tops out around 75 ft*lbs, then for 1\/2″, around 250 ft*lbs.<\/p>\n
\nIt’s hard to imagine me, personally, applying more than 250 ft*lbs of torque, but apparently that’s when 3\/4″ drive becomes relevant.<\/p>\n
\nSource:<\/p>\n