Mercedes, Toro Rosso, Force India, Red Bull to try F1 halo at Spa

The FIA decided last month to postpone the system's introduction to 2018 to allow for more time for development and testing.

Spa marks the start of the testing programme, which is set to involve all drivers running it at some point during the nine remaining races.

Up until this point, Sebastian Vettel and Kimi Raikkonen are the only race drivers to have run it and each only for installation laps.

Nico Rosberg, Carlos Sainz Jr, Nico Hulkenberg and Daniel Ricciardo will try it for their respective teams at Spa on Friday.

When asked by Autosport about Toro Rosso's programme for the halo test, Sainz said: "It's the installation lap for the moment and if I like it and it doesn't upset too much the rear wing, maybe I could proceed to run it a bit longer.

"It's the ideal track to try it out because it is where the visibility is tested.

"Through Eau Rouge is where you need to feel if it is a compromise or not.

"There are no concerns [going through Eau Rouge] because I will not be pushing flat out.

"It feels like they [the FIA] have listened to us as after Germany - we said we should all give it a try and give our opinion on it and it is good three drivers tomorrow are running it."

Rosberg, who has long been a supporter of plans to introduce a cockpit protection device, is looking forward to trying the system for the first time.

"I'll do one run, which will be a couple of laps," he said. "That is enough to understand if it's good or not.

"I massively support the direction of improving head safety but I'm not a fan of anything specific.

"I'll see how that goes to get an impression myself because I haven't tried it yet.

"It needs to go on as soon as possible if it is good, but I can only tell you on Friday."

Hulkenberg, who has previously said the halo "looks horrible", will run the device for a single installation lap and believes a long run will be required to get a full understanding of whether it is the right way forward.

"It's not going to be long, it's just going to be the installation lap but I do get an impression of the feeling from the inside having it on," he said.

"It's just about getting a feel for it and also get a read on certain things like visibility.

"To get a proper read and get a good understanding, you would have to run it longer than that for sure.

"Friday is only the first impression, the first read, so there is more to come later in the year."

Hulkenberg's team-mate Sergio Perez will run the device for an installation lap in first practice at Monza next weekend.