Haas and Williams have become the latest teams to incorporate T-wings onto their 2017 challengers as the first day of testing began in Barcelona.
Mercedes added a standalone T-wing to the W08 last week when Valtteri Bottas took to the Silverstone circuit for a filming session, but the aforementioned duo and Ferrari have opted to place the T-wing on top of their 'shark fin'.
There looks set to be a gradual roll-out of the T-wing between the other teams, with McLaren-Honda and Toro Rosso both confirming that they will fit one at some stage over the next four days.
"There is an area, one of the regulations boxes that wasn't covered in the way people expected when they were designing the regulations, which has allowed these T-wings to go in that area," chief engineer Peter Prodromou said at McLaren's launch.
"It is something we are looking at."