SMLE bolthead manufacturing process

[jmoore]

The trick MAY have been, especially with the "fully-treaded" SMLE types, to invert the thread cutter and run the lathe IN REVERSE

I would not be surprised that they were cut with the head fixed in place. Moving threading tool with spring retracting jaws/forming cutters that do the operation in one fell swoop. I think there's one in storage somewhere, but haven't seen it in years.