England scrum coach Neal Hatley insists Mako Vunipola's rapid set-piece improvement has transformed him into the complete player.
Alex Corbisiero, a distinguished predecessor in the Red Rose number one jersey, has acclaimed Vunipola as the best loosehead in world rugby on the strength of a rampaging start to the season at Saracens.
While the impact in open play of England's form player has never been doubt, his scrummaging was considered a potential weakness until the recent progress brought about by a technical adjustment.
"Mako has been absolutely outstanding for Saracens in the first half of the season," Hatley said. "There aren't many props in world rugby that can do what he does with the ball in hand.
"His set piece has come on immeasurably. Sometimes people get pigeon-holed as a carrying prop or a scrummaging prop and I think he crosses that divide.
"He's been very sound from a set-piece point of view. We've made a few little technical changes to his bind and that's had a real positive effect.
"There are a lot of good players around, but he's definitely getting there in terms of being the best loosehead in the world. If Corbs said that, it's a pretty good endorsement."
South Africa open the autumn series at Twickenham on Saturday while experiencing their worst run of results for a decade, including a record home defeat to New Zealand, but Hatley insists their threat must not be underestimated.
"They will probably go with a big pack and a big back five in the way they've tried to do for most of the year. It will be a good side," Hatley said.
"They have been a state of flux, but when they've played well they have been very impressive. The Lions did well in Super Rugby. We're expecting a good side to turn up.
"They have a very good scrum and will probably load up on that back five. There will be big bulk there so it will be a testing day from a scrum point of view."
England name their starting XV on Thursday morning, with Tom Wood set to edge Nathan Hughes for the openside duties.
Elliot Daly lined-up at outside centre during training on Tuesday and Hatley confirmed that Jonathan Joseph, his rival for the position and the more established option, is fully fit and available for selection.
Replacement scrum-half Danny Care has a minor shoulder injury, but will be fit to take his place on the bench.