Sergio Perez has topped the morning session at day two of testing in Barcelona, as the biggest talking point emerged from the Mercedes camp.
Video replays showed a system that the Silver Arrows are using, which changes the toe of the car by moving the steering wheel forwards and backwards along the straights.
Hamilton set the most laps of any drivers during the four hours of running, clocking an impressive 107 laps before handing over to Valtteri Bottas in the second half of the day.
Despite an interrupted morning for Renault, Daniel Ricciardo was second for Renault, four-tenths down on Perez.
The true pace of the Racing Point is not yet known due to the early stage that testing is in, however the car has caused a discussion due to its similarities to the Mercedes W10.
Red Bull was third with Alexander Albon, who headed Pierre Gasly and George Russell, who continues to show encouraging performances for Williams.
Charles Leclerc was sixth for Ferrari, ahead of Hamilton, who was central to the talk of the paddock during the morning.
Romain Grosjean was eighth in front of his former teammate Kimi Raikkonen, while Lando Norris rounded out the top ten for McLaren.
Sebastian Vettel is set to drive the car for the first time in the afternoon. Esteban Ocon will get another go in the R.S.20 following Ricciardo's stint this morning.